Fragmentation of 2,2,2-triphenylethoxychlorocarbene: evidence for ultrafast fragmentation-rearrangement in excited diazirines.
[reaction: see text] Photolysis of 3-(2,2,2-triphenylethoxy)-3-chlorodiazirine gives 2,2,2-triphenylethoxychlorocarbene which fragments with 1,2-phenyl migration and loss of CO and Cl(-) to yield the 1,1,2-triphenylethyl cation and thence 1,1,2-triphenylethene by proton loss. However, ps and fs laser flash photolysis provides evidence that up to 25% of the alkene product stems from carbocation that arises directly from excited diazirine rather than from the carbene.
Asymmetric Synthesis and Properties of Sulfinimines (Thiooxime S-Oxides).
Enantiomerically pure sulfinimines (thiooxime S-oxides 10), important building blocks in the asymmetric synthesis of amine derivatives, are prepared in good to excellent yields in one step from aromatic, heteroaromatic, and aliphatic aldehydes. This protocol involves treating commercially available (R)- or (S)-menthyl p-toluenesufinate (Andersen reagent 4) with LiHMDS, followed by the aldehyde, affording (E)-10 exclusively. The sulfinimines 10 are formed via a Peterson-type olefination reaction of silylsulfinamide anion 13 with the aldehyde. Anion 13 is generated by reaction of lithium menthoxide (12a) with bis(trimethylsilyl)sulfinamide 11, which is formed in the reaction of 4 with LiHMDS. The other product formed is O-(trimethylsilyl)menthol (12c), which is isolated in >80% yield for recycling. Two other less efficient methods for the asymmetric synthesis of 10 are discussed: (i) the asymmetric oxidation of sulfenimines 6 with chiral nonracemic oxaziridines and (ii) the reaction of metal aldimines, prepared from nitriles, with 4. All of these protocols fail with ketones.
STUDIES IN ISOUREAS AND ISOUREIDES: V. THE ADDITION OF DIHYDRIC AND SUBSTITUTED ALCOHOLS TO CYANAMIDE
In continuation of earlier studies on the formation of alkyl-isoureas by the addition of alcohols to cyanamide, a series of new isoureas has been prepared from ethylene glycol, glycol mono-ethyl ether, glycol mono-acetate, ethyl glycollate, ethanolamine, and resorcinol. In addition, the preparation of allyl-isourea, which had previously failed, m-nitrobenzyl- and cyclohexyl-isoureas was accomplished. The new isoureas were characterized by the preparation of salts (salicylates or benzoates), and of cyclic isoureides by condensation with acetoacetic and malonic esters. Some further study was made of benzyl- and phenylethyl-isoureas, previously prepared in this laboratory.