Oxidative transformations of cembrane diterpenoids III. Epoxycembrenes
Summary1. It has been established that the epoxidation of cembrene with perbenzoic and peracetic acids takes place stereospecifically at each of the trisubstituted double bonds with the formation of 4S,5R-, 7S,8S-, and 11S,12S-monoepoxycembrenes, the structures and absolute configurations of which have been established by spectral methods.2. Epoxidation of cembrene at the C11–C12 double bonds under the conditions used takes place preferentially as compared with epoxidation at the C7–C8 double bond.
New methods for the preparation of 1-phenyl-trans-cyclohexane-1,2-diol
Abstract In contrast with previous reports, it was found that the reaction of 1-phenylcyclohexene with peroxyformic acid is not entirely stereospecific, but gives some trans -1-phenylcyclohexane-1, 2-diol (IV) beside the cis -isomer (III). The reaction of 1-phenylcyclohexene oxide (II) with formic acid yielded a similar mixture of III and IV, while addition of trichloroacetic acid in benzene was entirely cis -stereospecific. Reaction of the epoxide II with potassium hydroxide took place only under very drastic conditions to give a small yield of III, while sodium 2-dimethylaminoethoxide added exclusively in a trans way, leading to the amino ether X, which was easily transformed into the trans -glycol IV. The latter compound was also the main product of the borohydride reduction of 2-hydroxy-2-phenylcyclohexanone (IX). Possible explanations of the observed stereochemical results are discussed.
The direction of ring opening of trans-α-methylstilbene oxide by organic acids
Abstract In the reaction of mesitoic acid with trans-α-methylstilbene oxide the anion adds exclusively to the tertiary carbon atom, to give the hydroxy ester of type III, which also can be prepared from α-methylbenzoin mesitoate with KBH4 and is transformed into the isomeric ester of type V by the action of alkali; the latter ester also being formed by reaction of threo-1,2-diphenyl-1,2-propanediol with mesitoyl chloride. Other acids yields only esters of type V, probably formed from primary products of type III by a rapid acyl group shift. All esters thus prepared belong to the threo series; corresponding erythro esters were prepared for comparison. The reductions of α-methylbenzoin acetate and mesitoate with LiA1H4 produce exclusively threo-1,2-diphenyl-1,2-propanediol, in contrast with the low stereoselectivity of the similar reduction of α-methylbenzoin itself.