Enantioconvergent syntheses of two classes of chiral cyclopentenyl sulfone synthons

Multiply convergent syntheses via conjugate-addition reactions to cycloalkenyl sulfones

“…This bromohydrin was smoothly converted to epoxide 64 upon basic workup (74% yield from l-55). 20 The overall transformation is formally equivalent to a stereospecific sulfide-directed epoxidation in which the sulfur moiety has been retained in a potentially useful low oxidation state.…”

“…Alternatively, alcohol-directed epoxidation followed by mesylation produces (-68 which yields the enantiomeric epoxy vinyl sulfone d-57 after elimination of the mesylate.20 Thus, enantioconvergent methodology is available to provide either enantiomer of epoxy vinyl sulfone 57 from either enantiomer of sulfide-alcohol 55. 20 cis-and trans-hydroxy vinyl sulfones d-58 and d-66 comprise another pair of diastereomers which can be effectively converged to the same enantiomeric series.…”

“…Individual treatment of these two materials with dimethylamine affords the same amino vinyl sulfone (-72. Presumably this reaction proceeds via the intermediacy of 71. 20 Compound (-72 serves as a progenitor for a pair of key substrates in our synthetic program. Quaternization of the amino moiety of (-72 affords ammonium salt 73 (similarly, reaction of the fert-butyldiphenylsilyl analogue of (-72 yields 74 which is best stored as its fluoroborate salt21®).…”

Chiral Preparation of C2-Symmetric 4-Cyclopentene-1,3-diol

“…But, because of the difficulty of stereoselectively constructing trans-diol functionalities on a cyclopentene ring, no efficient chiral preparation of C 2 -symmetric 4-cyclopentene-1,3-diol (2) has been reported, except for a report by Kurozumi 5 and one by Fuchs. 6 Kurozumi et al reported that asymmetric hydrolysis of a stereoisomeric mixture of diacetate 3 using baker's yeast furnished (-)-2 in 7-17% yield with 10-32% optical purity (Scheme 1). On the other hand, Fuchs et al obtained (+)-2 from chiral sulfide alcohol 4 with 90% ee, via [2,3]-sigmatropic rearrangement of sulfoxide 5 as the key step.…”

(1S,6S)-2-(Phenylsulfonyl)-7-oxabicyclo[4.1.0]-hept-2-ene

“…PhSO 2 CHD-epoxide reacts with alkyl lithium reagents to produce vari-ous addition adducts and 3-benzenesulfonyl-cyclohexa-2,4-dienol in modest yield. 7 The conversion was considerably improved by exposing the epoxide to LiHMDS to furnish the dienol in quantitative yield (eq 2). The emergent alkoxide can be protected in situ with tert-butyldimethylsilyl chloride in the same yield.…”