Symmetric Diarylsulfoxides as Asymmetric Sulfinylating Reagents for Dialkylmagnesium Compounds

Abstract

At −78 °C, primary dialkylmagnesium compounds reacted with diarylsulfoxides when 1.5 equiv of the dilithium salt of (S)-BINOL was added as a promotor. Alkyl aryl sulfoxides resulted in up to quantitative yield and with up to 97% ee. This demonstrates the feasibility of asymmetric sulfinylations by achiral sulfinylating agents (from the perspective of Alkyl2Mg) as well as the feasibility of asymmetric sulfoxide–magnesium exchanges (from the perspective of Ar2SO).

Prochiral Diheteroaryl Sulfoxides and Their Reactions with (S)‐Li2‐BINOLate‐Activated Diisobutylmagnesium

“…of Li 2 ‐ 9 . This procedure had worked best starting from isocyclic diaryl sulfoxides . “Treatment B” was like “treatment A” but confined to the stoichiometrically required amount of 0.5 equiv.…”

“…Preparation of an i Bu 2 Mg Solution in Et 2 O: Ref . (which, in turn, was based on the procedure by which we had prepared i Pr 2 Mg in Et 2 O earlier).…”

“…The leaving group, which is expelled after the organometallic attacks the S‐atom and thereby forms a λ 4 ‐sulfurane, is a different organometallic; it persists until it is quenched – usually during workup. The top of Scheme illustrates our recent variation of this strategy: the asymmetric sulfinylation of mixtures of dialkylmagnesium compounds and dilithio‐( S )‐BINOL (Li 2 ‐ 9 ) with symmetric isocyclic diaryl sulfoxides 6 , . This provided alkyl aryl sulfoxides 5 in up to 100 % yield with up to 97 % ee .…”

“…Either strategy involves symmetric diaryl sulfoxides as sulfinylating agents, dialkylmagnesium compounds as pre‐nucleophiles, and Li 2 ‐( S )‐BINOLate (Li 2 ‐ 8 ) both as a promoter and inducer of enantiocontrol. The best‐performing dialkylmagnesium of our earlier investigation was i Bu 2 Mg . Therefore, we stayed with it here, too.…”

“…Established technique (top): Asymmetric syntheses of alkyl aryl sulfoxides 5 from isocyclic diaryl sulfoxides 6 , . Objective of current study (bottom): Asymmetric syntheses of alkyl heteroaryl sulfoxide sulfoxides 5′ – simplified models of compounds 1 – 4 (Figure ) – from heterocyclic diaryl sulfoxides 6′ …”