despite its potential for use in organic synthesis , applications of tmsccl3 ( tms = sime3 ) have been far narrower in scope than those of closely related tmscf3 ( ruppert  prakash reagent).1 two reasons can be identified as the origins of this situation . firstly , all present literature preparations of tmsccl3 provide either low - to - modest isolated yields,2 or rely on extreme low - temperature protocols ( typically 110  c),2 limiting easy access to this reagent . secondly , most applications of tmsccl3 require its  activation  by a silylphilic promoter , typically a fluoride ion . the intimate mechanism(s ) by which this process proceeds are presently based on ad hoc suggestions rather than tangible data . in such environments it is possible to select reaction conditions that may not be mechanistically optimal . although tmsccl3 is known to participate in a small number of 1,2-additions to aldehydes,3 ketones3 and imine derivatives ( scheme  1),4 1,4 addition modes are practically unknown and are limited to just six examples , with modest yields , in a single paper by cunico and zhang.5 we were interested to identify improved experimental conditions for such reactions and to understand the underlying mechanism of 1,4-addition of tmsccl3 . new access to -ccl3-substituted nitroalkanes is of interest , and sosnovskikh et  al . , and others,6 have developed a range of unusual and useful methods around this motif . for the conjugate - addition mechanistic investigations we required access to large amounts of highly pure tmsccl3 . unfortunately , current literature preparations2 have significant limitations , either in yield , purity of reagent attained , reproducibility or the need for special conditions . these issues are due to the fragility of mccl3 ( typically m = li or na ) intermediates . 0.1 per ml ) as a co - solvent ( 5  equiv ) would significantly enhance ccl3 capture , improving the tmsccl3 yield . addition of lihdms ( lithium hexamethyl disilazide ) in hexane / thf ( 65:20 ) to a chloroform / tmscl ( 12:64 ) mixture at 65  c , followed by slow warming to ambient temperature proved optimal . after an appropriate workup , kugelrohr sublimation routinely afforded pristine material in 6470  % yield on a > 10  g scale . the nitroolefins , 1 , for our study were prepared by using a one - pot procedure by dauzonne and royer,7 a condensation method by andrew and raphael8 or by using a very recent agno2 method by maiti et  al.9 ( scheme  2 ) . the advantage of the former two methods , although the yields are often modest , is that they are technically simple and provide a direct route to the 3-nitro-2h - chromenes and styrenyl systems , respectively . initial studies on substrate 1  a ( table  1 ) confirmed the findings of cunico and zhang,5 but indicated that csf is an unreliable promoter because of its low solubility in organic solvents . soluble nbu4x [ x = cl , oac , f and especially ph3sif2 ( tbat ) ] were found to be efficient promoters at 5  mol  % in both polar ( thf , entries  25 ) and non - polar ( toluene , entries  610 ) solvents . the less - silylophilic promoter , nbu4br , led to a very slow turnover . due to the speed of the reactions in thf at 20  c no rate estimates could be attained ( entries  25 ) . however , approximate initial rates ( based on conversion in the first 20  sec ) could be attained in toluene , confirming the high efficacy of tbat ; in the absence of any promoter no reaction occurred . the spectroscopic properties of 2  a are in accord with 1,4-addition of the trichloromethyl group . in particular , a characteristic multiplet is seen at h=5.56  ppm in the h  nmr spectrum , correlating to the c  nmr ch signal  to the nitro group at c=80.7  ppm . the -ch group is diagnostically shifted to lower frequency ( c=56.3  ppm in 2  a ) compared with its cch precursor ( c=139.2  ppm in 1  a ) , whereas a low - intensity quaternary signal at c=100.8  ppm is assigned to ccl3 and the molecular ion of 2  a shows the expected cl3 isotope pattern . promoter comparison for tmsccl3 addition to 1  a. [ a ]  carried out on 0.3  mmol 1  a ( 0.06  m ) . yield data obtained from gc analysis in the presence of an internal standard ( 1-methylnaphthalene , 25  l , 0.18  mmol ) . [ b ]  use of either solvent resulted in inefficient catalysis ; [ c]>95  % of 2  a could only be attained after 24  h in thf with excess csf ( 3.75  equiv ) . the conditions of table  1 ( entry  5 ) could be applied to a range of nitroalkene substrates , leading to various 1,4-addition products in 3795  % isolated yields ( scheme  3 ) . for the acyclic systems reversal of the addition mode isolated addition products from tbat - catalysed ( 5  mol  % ) additions of tmsccl3 to nitroalkenes 1 . the connectivity of 2  d could be confirmed by an x - ray crystallographic study ( figure  1 ) . in comparison , the 27 structures in the cambridge crystallographic database6 showing the same no2chchccl3 motif have : nc 1.491.53 , cc 1.521.55 and cccl3 1.511.57   ; n- c - c 105.8117.1 and c - c - ccl3 111.2117.1  . two closely related six - ring structures ( cibgif and hacjay ) show anti arrangements , as in 2  d , but a syn motif is also known ( qemzue).6 molecular structure of 2  d. selected interatomic distances and angles : c(1)c(4 ) 1.556 , c(3)c(4 ) 1.544 , n(1)c(3 ) 1.519   ; c(1)-c(4)-c(3 ) 109.2 , n(1)-c(3)-c(4 ) 111.3  . the following scope and limitation comments should be made : i ) addition of tmsccl3 to the substrate and tbat catalyst was appropriate for -substituted substrates 1  a  e and 1  q. however , for terminal nitroalkenes ( 1  f  p ) the alkene needed to be added slowly ( over 1  h ) to tmsccl3/tbat mixtures to avoid polymerisation , which led to unacceptable yields of 2 . ii ) acyclic -substituted nitroalkenes led to very poor reactions and this substrate class was not further pursued ; -substitution provided clean products ( e.g. 2  m ) , but in reduced yield . iii ) although alkyl , ether , ester , alkene and cf functional groups were tolerated in various degrees , some aryl bromide - containing substrates ( e.g. 8-bromo-3-nitro-2h - chromene ) and benzylic ( e)-bnchchno2 were not tolerated and led only to decomposition . given the known relative stability of the ccl3 radical , and its propensity to add to unsaturated systems ( kharasch et  al.10 ) , tests were carried out to assess the veracity of such reaction pathways . firstly , it was observed that the presence of the known radical inhibitors hydroquinone or butylated hydroxytoluene ( bht ) did not prevent tbat - catalysed additions to 1  d under strictly anaerobic conditions . secondly , the substrate 1  r was used to provide potential intramolecular radical trapping sites . the standard reaction conditions ( slow addition of 1  r to tmsccl3/tbat under argon ) led to trace amounts ( 15  % ) of bicyclic 2  r , and the majority of the starting material remained unconverted after the typical reaction time of 116  h ( scheme  4 ) . however , if the reaction was conducted under aerobic conditions 2  r became the major product . tmsccl3 solutions in thf , in the presence of tbat and o2 ( one molar equivalent of oxygen injected into a sealed reaction ) , were analysed by si nmr spectroscopy and revealed a significant amount of a single silicon - containing species showing si=7.4  ppm . based on comparison with literature silicon nmr shift values11 we assigned this new species as tms2o . one explanation for the formation of 2  r is reaction of tmsccl3 ( in the presence of tbat ) with o2 , leading to tms2o2 and ccl3 radicals that cascade to 2  r , via 3 and 4 . although we could not detect any tms2o2 peroxide ( si27  ppm12 ) in air or in o2-exposed samples of tmsccl3 , in the presence or absence of tbat , the latter was rapidly converted to tms2o . it is likely that any peroxide would be both generated and decomposed as shown in scheme  4 . literature bicycles related to 2  r have been generated , either by oxidation of nitronate anions13 or through nitrile oxide formation and subsequent [ 2 + 3 ] cycloaddition chemistry,13 from the expected 1,4-addition product 5 . although we can not completely exclude such possibilities , such approaches normally require stronger oxidants than molecular oxygen or prolonged heating at 60  c.13 the connectivity of 2  r could be confirmed by an x - ray crystallographic study on its dehydrochlorination product 2  r , obtained through simple mgso4 drying / recrystallisation of 2  r ( figure  2 ) . formation of the cccl2 bond is also evident in the c  nmr spectrum , in which the diagnostic ccl3 signal at c=99.4  ppm in 2  r is replaced by two quaternary alkene signals ( c=121.4 and 126.7  ppm ) . both 2  r and 2  r have a cn resonance ( c=167.6 and 166.5  ppm , respectively ) . the structure of 2  r is reminiscent of other tetrahydro-3h - cyclopenta[c]isoxazoles in the cambridge crystallographic database.14 aerobic cyclisation of substrate 1  r. molecular structure of 2  r. selected interatomic distances and angles : n(1)c(6a ) 1.258 , n(1)o(2 ) 1.431 , c(6)c(7 ) 1.324   ; c(6a)-n(1)-o(2 ) 107.5 , c(7)-c(6)-c(6a ) 127.1  . despite the aerobic cyclisation shown in scheme  4 in particular , the observation of low , but reproducible , ee values in the formation of 2  q by using chiral promoters at low substrate conversion suggested that a different reaction mechanism operates under o2-free conditions . to the best of our knowledge , no study of the explicit reaction mode of tmsccl3 with nbu4siph3f2 ( tbat ) has been carried out , therefore , we sought to define the non - radical process by multi - nuclear nmr studies . reagent concentrations of 0.125  m in thf/[d6]benzene ( 5:1 ) at 20  c offered the best compromise with respect to solubility , si sensitivity and attainment of o2-free conditions . temperatures of 20  c are also the lowest at which viable catalytic reactions are possible , indicating that the reactions should be slowed to only primary events at this temperature . in an initial set of conditions at 20  c , tmsccl3 ( si=21.9  ppm ) was immediately converted to tmsf ( si=32.4  ppm)15 on addition of tbat ( si=108.8  ppm),16 which itself was transformed to ph3sif ( si=4.1  ppm)17 ( figure  3 ) . no other silicon - containing species were present , except for traces of tms2o ( si=7.3  ppm)11 ( which could be minimised / eliminated by good experimental technique to eliminate the last traces of o2 ) . the jsif coupling pattern is indicative of the number of attached fluorine atoms in these species . the residual tbat species , tmsf and ph3sif could be correlated to signals at f=98.9,17 158.015 and 170.5  ppm16 in the f  nmr spectrum of the reaction mixture at 20  c ( see the supporting information ) . the si and f  nmr spectra of the same reaction mixture at + 20  c show only very slight broadening , indicating that any exchange between the species detected is , at best , very slow under the reaction conditions . at 20 c the c  nmr spectrum of the tmsccl3/tbat mixture , in the methyl region , confirmed the presence of me3sif ( c=0.4  ppm , jcf=15.5  hz ) and a singlet peak ( c=1.6  ppm ) ascribed to the expected exchange product , nbu4ccl3 . this latter compound is stable at 20  c indefinitely , no evidence of formation of tetrachlorethene ( c=120.7  ppm ) , or any other ccl3 or dichlorocarbene - derived byproducts was seen in the spectra . no reaction was observed when nitroalkene 1  a was added last to the above mixture , which was then warmed from 20 to 0  c ( conditions under which the catalytic reaction is spontaneous ) . si nmr spectra ( 79.5  mhz , 5:1 thf/[d6]benzene , 20  c ) : a )  tmsccl3 ( =21.9  ppm ) ; b ) tbat ( =108.8  ppm , j(sif)=254  hz ) ; c ) a nominal 1:1 mixture of tmsccl3/tbat ( a slight excess of tbat was used to provide a spectral internal standard ) , tmsf ( =32.4  ppm , j(sif)=275  hz ) , tms2o ( =7.3  ppm ) , ph3sif ( =4.1  ppm , j(sif)=282  hz ) . in a separate set of conditions , nitroalkene 1  a was first added to tmsccl3 at 20  c . the h  nmr spectrum in the region h=6.88.0  ppm contains the aryl and alkene signals of 1  a ( see figure  4  a , b ) . the signal of tmsccl3 is at h=0.20  ppm ( not shown in figure  4 ) . the equivalent c  nmr spectra confirm < 5  % reaction of alkene and tmsccl3 because only the characteristic peaks of 1  a and tmsccl3 , at c=4.5  ppm are present . subsequent addition of tbat at 20  c to this mixture leads to partial ( 38  % ) , but immediate , conversion of 1  a into a new compound with h ( figure  4  c ) and c  nmr spectra ( see the supporting information ) that are closely related to those of the addition product 2  a. this new species is assigned as nitronate 8 ( scheme  5 ) . in some experiments traces of a new species could be detected before the addition of tbat ( see figure  4  b ) . this species could only be identified as a product of nitroalkene decomposition , or species 6 ( see below ) . partial h  nmr spectra ( 5:1 thf/[d6]benzene , 20  c ) : a ) alkene 1  a ; b ) a nominal 1:1 mixture of alkene 1  a and tmsccl3 ; c ) after addition of 1  equiv of tbat to mixture ( b ) . signals due to tbat are marked (  ) , those due to ph3sif (  ) and those due to the proposed nitronate product 8 (  ) . overall , the data from the stoichiometric nmr experiments are in accord with scheme  5 . once formed , nbu4ccl3 is insufficiently nucleophilic to directly attack the nitroalkene and equilibration back to tmsccl3 is not possible . rather , the nitroalkene binds tmsccl3 by means of an electron - rich no contact , providing 6 . we could detect no exchange broadening of the minor signals observed in figure  4  b from ambient temperature down to 20  c . further cooling of the reaction was not possible because of the formation of non - homogeneous samples , and heating the sample was not possible . however , the data are generally in accord with attack of an external nucleophile , in this case fluoride ions ( either directly or indirectly from tbat18 ) , on 6 , triggering ccl3 transfer , presumably through a chair - like transition state , leading to 7 . finally , due to the strength of the sif bond in tmsf ( and the clear lack of exchange with this species in the nmr studies ) if the conclusions of the stoichiometric reactions shown in scheme  5 can be translated to the catalytic reactions , three clear predictions can be made : i ) nitronate anions themselves should be excellent promoters of the reaction . ii ) if the concentration of nitronate ( or indeed any other anionic promoter nucleophile ) builds up over time , a wide range of nucleophilic promoters ( nu ) will be available to replace fluoride ( f ) in the key conversion of 6 into 7 ( scheme  5 ) . iii ) under such conditions , the ee value of the 1,4-addition product , produced by an asymmetric source of nu should decrease over time ( due to competition with an increasingly populated pool of promoter anions ) . to check these suppositions we prepared nbu4[ch2no2 ] from nitromethane and found that it does indeed promote rapid quantitative conversion of 1  a into 2  a. the chiral complex [ ni(duphos)2](acac)2 ( duphos=(r , r)-methylduphos , cas [ 147253 - 67 - 6 ] ; acac = acetylacetonate ) was found to be an , albeit poor , promoter of asymmetric trichlomethylation of 1  q ( see the supporting information ) . nevertheless , the ee value of 2  q formed by using this catalyst ( 10  mol  % ) does decrease reproducibly from 15 to < 1  % over 20  h , in line with predictions . the bifunctional chiral catalyst by takemoto et  al.19 ( 10  mol  % ) , associated with tbaf as a co - promoter ( 10  mol  % ) , also led to a decrease in the ee value of 2  q over time ( from 26  % to < 1  % ) . based on all of the data it seems likely that scheme  6 is the most rational description of the catalytic cycle . the nitronate product , 8 , can either act as a promoter itself or leave the promoter pool by means of a reaction with either tmsx ( x = ccl3 or nu , if nu is a suitable leaving group ) . proposed catalytic cycle . finally , the use of the 1,4-addition products , 2 , for the formation of other products was briefly investigated . treatment of 2  a with kotbu in thf led to the formation of dichlorocyclopropane 9 in moderate yield ( scheme  7 ) , through -ch deprotonation . for example , 2  f led to the formation of dichloroalkene 10 when treated under the same conditions . catalytic 1,4-additions of tmsccl3 to electron - deficient michael acceptors have considerable potential for use in organic chemistry . the mechanistic studies presented here are consistent with pre - coordination of the nitroalkene to the silicon reagent before its promotion by a silylphilic nucleophile . attempts to develop asymmetric versions of this reaction will prove to be challenging for mechanistic reasons . the kinetically derived nitronate product of the reaction is itself a highly effective chain carrier , and attaining a competitive chiral catalyst or alternative conditions will be critical for success . full details of all transformations and associated spectroscopic data are given in the supporting information . nitroolefins 1  a  e were prepared by dauzonne and royer s one - pot procedure7 . alkene 1  a showed identical spectroscopic properties to previously reported samples.20 compounds 1  b  e , previously unreported , were fully characterised ( see the supporting information ) . nitroolefins 1  g l were prepared by andrew and raphael s condensation method8 and had identical spectroscopic properties to previously reported samples.9 ,  21 ,  22 nitroolefins 1  m  r were prepared by the agno2 method by maiti et  al.,9 and had identical spectroscopic properties to previously reported samples.9 ,  23 trimethyl(trichloromethyl)silane ( tmsccl3 ; 0.21  g , 1.1  mmol ) in thf ( 2  ml ) was added dropwise to a solution of the cyclic nitroalkene ( 1  mmol ) and tetrabutylammonium triphenyldifluorosilicate ( tbat ; 0.027  g , 5  mol  % ) in thf ( 2  ml ) under argon at room temperature , and the reaction mixture was stirred overnight . the mixture was concentrated in vacuo and then purified by flash chromatography on silica gel to give the corresponding michael addition products . alternatively , the reactions were quenched with saturated nh4cl ( aq ) , extracted with ethyl acetate , dried over anhydrous mgso4 and concentrated before purification by chromatography . the acyclic alkene ( 1  mmol ) in thf ( 2  ml ) was added dropwise , over a period of one hour , to a solution of trimethyl(trichloromethyl)silane ( tmsccl3 ; 0.21  g , 1.1  mmol ) and tetrabutylammonium triphenyldifluorosilicate ( tbat ; 0.027  g , 5  mol  % ) in thf ( 2  ml ) under argon at room temperature , and the mixture was stirred overnight . the mixture was concentrated in vacuo and then purified by flash chromatography on silica gel to give the corresponding michael addition products . trimethyl(trichloromethyl)silane ( tmsccl3 ; 0.21  g , 1.1  mmol ) in thf ( 2  ml ) was added dropwise to a solution of the cyclic nitroalkene ( 1  mmol ) and tetrabutylammonium triphenyldifluorosilicate ( tbat ; 0.027  g , 5  mol  % ) in thf ( 2  ml ) under argon at room temperature , and the reaction mixture was stirred overnight . the mixture was concentrated in vacuo and then purified by flash chromatography on silica gel to give the corresponding michael addition products . alternatively , the reactions were quenched with saturated nh4cl ( aq ) , extracted with ethyl acetate , dried over anhydrous mgso4 and concentrated before purification by chromatography . the acyclic alkene ( 1  mmol ) in thf ( 2  ml ) was added dropwise , over a period of one hour , to a solution of trimethyl(trichloromethyl)silane ( tmsccl3 ; 0.21  g , 1.1  mmol ) and tetrabutylammonium triphenyldifluorosilicate ( tbat ; 0.027  g , 5  mol  % ) in thf ( 2  ml ) under argon at room temperature , and the mixture was stirred overnight . the mixture was concentrated in vacuo and then purified by flash chromatography on silica gel to give the corresponding michael addition products . as a service to our authors and readers , this journal provides supporting information supplied by the authors . such materials are peer reviewed and may be re - organized for online delivery , but are not copy - edited or typeset . technical support issues arising from supporting information ( other than missing files ) should be addressed to the authors