Useful Chiral Auxiliaries for the Synthesis of Chiral Oxiranes

Aggarwal et al. have reported an asymmetric synthesis using the sulfur ylides generated in situ by treating the sulfonium salts 3 and 4 prepared from (1R,4R,5R)-4,7,7-trimethyl-6-thiabicyclo[3.2.1]octane (1), with bases. According to their results, the reactions of 3 with aldehydes and imines afford the corresponding chiral oxiranes and aziridines, respectively, in high yields with diastereo- and enantioselectivities.¹⁾ On the other hand, the reactions of 4 with aldehydes also give excellent yields of the corresponding α,β-unsaturated oxiranes with perfect stereoselectivities.¹⁾ Moreover, this methodology was also successfully applied to the total synthesis of alkaloids, such as quinine.¹⁾
Thus, 1 and 2 are useful chiral auxiliaries applicable to the synthesis of various oxiranes and aziridines via sulfur ylides.