Alkylidenation with sulfoximines

The methylation of sulfoximines 45 with Me30BF4 proceeded readily and gave the corresponding cyclic aminosulfoxonium salts 46 in quantitative yields. Upon treatment with LiN(H)t-Bu first at-78 °C and then at room temperature, salts 46 delivered the enantio- and diastereomerically pure bicyclic 2,3-dihydrofurans 50 cleanly in high overall yields. It is proposed that the reactions of the aminosulfoxonium salts 40 and 46 with the lithium amide at low temperatures afford the vinyl aminosulfoxonium ylides 41 and 47, respectively. These alkylidene carbenoids eliminate sulfinamide 35 at higher temperatures with formation of the alkylidene carbenes 42 and 48, respectively. Subsequently, the alkylidene... 

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