Stereoselective conjugate additions of sulphoxide stabilised carbanions to α,β-unsaturated esters

Enantioselective Synthesis of Benzyl tert‐Butyl Sulfoxides

“…There are several synthetically useful methods to remove the sulfinyl group subsequent to the α‐substitution,7–9 and therefore, it may be regarded as a chiral auxiliary for carbanions. Earlier, we showed that sulfoxide‐stabilized carbanions undergo efficient regioselective conjugate addition to α,β‐unsaturated esters and ketones, generally resulting in excellent diastereoselectivity (Scheme ) 10,11. As expected, the nonacidic group on the sulfoxide, referred to as the “spectator group” (R 1 in Scheme ), has a pronounced effect on the yield and diastereoselectivity in these reactions.…”

Highly Stereoselective Conjugate Additions of Heteroaryl Alkyl Sulfoxides

“…Coordination of the nitrogen of the spectator group to the counterion may be a prerequisite for the high diastereoselectivity, because aryl spectator groups which lack this possibility generally give very poor selectivity. 5 Second, the remarkable improve-ment in diastereoselectivity on changing from dialkylamide to hexamethyldisilazide bases is unprecedented in sulfoxide chemistry. 12 We tentatively suggest that it may be related to the ability of the corresponding amines to ligate the metallated sulfoxides.…”

“…In contrast, alkyl t-butyl sulfoxides gave anti, anti adducts. 5 The benzyl imidazolyl sulfoxide 1d failed to react with methyl crotonate, but gave a good yield of diastereomerically pure conjugate adduct 2i with chalcone (Entry 7). The stereochemistry of this adduct is tentatively assigned by analogy with that of the alkyl adducts.…”

“…4 The carbanions formed from some sulfoxides react cleanly with a,b-unsaturated esters to give conjugate adducts with good diastereoselectivity. 5,6 The t-butyl spectator group gave much better results than the more commonly used p-tolyl for both alkyl and benzyl sulfoxides. 7 The yields and stereoselectivity were excellent for benzyl tbutyl sulfoxides, and the sulfinyl group can be removed reductively, or by intramolecular displacement to give lactones, 8 so t-butyl is the spectator group of choice in this series.…”

Synthetically Useful Desulfurisation Reactions of Heteroaryl Sulfoxide Conjugate Adducts

“…5 In the case of alkyl sulfoxides (R 2 = alkyl), as reported in the accompanying Letter, the yields and stereoselectivity of the conjugate additions are excellent using 1-methyl-2-imidazolyl and 2-pyridyl as spectator groups, 6 and somewhat inferior using t-butyl. 7 Good results have also been achieved using p-tolyl 2-(trimethylsilyl)ethyl sulfoxide. 8 We now report significant new developments highlighting the ease of removal of heteroarylsulfinyl auxiliaries by reductive desulfurisation and thermal elimination.…”