Sulfone lithiation approach

Similarly, Rodriguez et al. [81] have used an iterative sulfone lithiation approach to synthesize a range of aliphatic 5,5-spiroacetals (Scheme 36). Acylation and... 

Scheme 36 Rodriguez et al. s sulfone lithiation approach toward spiroacetals [81]...

Addition of Lithiated Sulfoxides and Sulfones Nucleophilic addition of lithiated methylaryl sulfoxides (384) to nitrones of various structures proceeds easily and in good yields (622). The reactions are applied to the synthesis of optically active a-substituted and a,a-disubstituted hydroxylamines, to secondary amines (623), and to enantioselective syntheses of alkaloids (624). The preferred approach to (+ )-euphococcinine is based on the use of homochiral 3-sullinyl nitrones (385) (Scheme 2.167). 

Nucleophilic addition of lithiated sulfones to nitrones made it possible to develop new stereoselective approaches to the synthesis of pyrrolidine-N -oxides based on a reverse-Cope-type elimination. One method is based on the reaction of lithiated sulfones with nitrones (386) (Scheme 2.168) (625). 

Another approach is based on the condensation of lithiated sulfones to unsaturated nitrones (387). Good yields of single stereoisomers of unsaturated hydrox-ylamines (388) are obtained. They undergo a reverse-Cope elimination leading to a single enantiomer of pyrrol idine-/V -oxide (389) (Scheme 2.169) (626). 

Bruckner s approach started from L-arabinose converted in five steps to allylic alcohol 175, and to alkoxy sulfone 176 thereafter (Scheme 23). Key [2, 3] Wittig rearrangement of lithiated 176 in the presence of allyl lithium led to the desired compound 178 and its C17 isomer (ratio 1.4 1) via the intermediate 177. Regioselective epoxidation and thiophenate epoxide ring opening furnished sulfide 179 transformed in four steps to the C14-C20 building block 180. 

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