Stereoselective conjugate additions of benzyl sulphoxides to α,β-unsaturated esters

Enantioselective Synthesis of Benzyl tert‐Butyl Sulfoxides

“…of t BuOK. The results for these one‐pot reactions compare favorably with those obtained by formation of the sulfoxide followed by a separate reaction with the electrophiles 10,11,38,39. In contrast to these results, we found that when benzylic sulfoxides are formed using Grignard reagents under the conditions described earlier, in situ deprotonation does not occur.…”

“…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.…”

“…In the case of methyl crotonate, the product of two consecutive conjugate additions was obtained, even after short reaction times. These results are in striking contrast to the efficient stereoselective conjugate additions observed using lithiated sulfoxides generated by deprotonation with LDA (lithium diisopropylamide)11 and again highlight the marked effect of the potassium alkoxide additive. Optimization of the reaction conditions revealed that reducing the amount of t BuOK to 0.8 equiv.…”

Highly Stereoselective Conjugate Additions of Heteroaryl Alkyl Sulfoxides

“…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

“…The choice of "spectator" group (R 1 below) attached to the sulfinyl group strongly influences the reactivity of the sulfoxidestabilised carbanions, the stereoselectivity of their reactions, and the ease of removal of the auxiliary. 3 t-Butyl is the spectator group of choice for benzyl sulfoxides (R 2 = aryl), 4 because it gives excellent yields and stereoselectivity, and the sulfinyl group can be removed reductively, or by intramolecular displacement to give lactones. 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.…”