Kinetically controlled, stereoselective formation of vinylic sulfones by conjugate addition of lithiated 3-alkylallylic sulfones to cyclic enones

Enantioselective, Cyclopentene-Forming Annulations via NHC-Catalyzed Benzoin−Oxy-Cope Reactions

“…As previously suggested by Nair, 5 would undergo tautomerization, stereoselective intramolecular aldol addition, lactonization, and decarboxylation to afford cyclopentene product 7 . Indeed, a similar cyclopentanone-forming aldol cascade initiated by an anionic oxy-Cope reaction has been reported, and formal conjugate additions of allylic anions to enones that proceed via 1,2-addition/oxy-Cope rearrangement are well-known 1 Cyclopentenes via NHC-Catalyzed Oxy-Cope RAR …”

The Julia Reaction

“…Examination of the literature reveals that Michael additions are usually facilitated when the carbanion is made softer by delocalization into a strongly electronwithdrawing group [61][62][63][64][65][66][67][68], when the enolate resulting from 1,4-addition is particularly stable [69], when the addition reaction is performed in the presence of HMPA [70][71][72], or when the 1,2-addition is disfavored by conformational effects [73,74]. A few examples of such sulfonyl anions are collected in Scheme 3.17.…”

A General Synthesis of Methylenecyclopentanes by a Stereoselective [3 + 2] Approach

“…The stereochemical assignments for 17 rely on NOE data (Figure ). Previously reported reactions of other allylic sulfones with cyclohexenone at low temperature and in the absence of HMPA afforded mainly 1,2-carbonyl addition products. , We did not detect such products, but the selectivity of this conjugate addition was not as high as with acyclic acceptors: along with 14 , originating from the cyclization of the erythro -diastereomeric adduct, minor amounts of open-chain adduct 15 , with the tentatively assigned threo -configuration, , and of the vinylic sulfone 16 (a γ-adduct) were also isolated. The assigned cis -fusion for the hydrindanone derivative 14 (entry 1) is based on NOE data (Figure ).…”

“…In order to rationalize the anti -diastereoselective 12 outcome of the initial conjugate addition step, the well-documented sensitivity of Michael reactions to the steric environment should be taken into account along with chelation control in the transition state (TS), via coordination of the lithium counterion with the oxygens of the sulfone and the carbonyl group …”