2000 stereochemistry

stereochemistry (general, optical resolution)O 0030

15 - 031Highly Diastereoselective Asymmetric Thio-Claisen Rearrangements.— Using C2-symmetric pyrrolidines as removable chiral auxiliaries, the thio-Claisen rearrangements of thioamides such as (I) with allylic bromides is studied.With bromides (II), one new stereogenic center is formed to give products (III)with moderate to high diastereoselectivities. If (E)- or (Z)-allylic bromides(IV) or (VI) are applied, the alkylations proceed with high syn:anti selectivities(94-96% d.e.) and with good to excellent asymmetric induction (66-99% d.e.).The cleavage of the chiral auxiliary under reductive hydrolysis conditions isdemonstrated for derivative (VIIb). — (HE, SHUWEN; KOZMIN, SERGEYA.; RAWAL, VIRESH H.; J. Am. Chem. Soc. 122 (2000) 1, 190-191; Dep.Chem., Univ. Chicago, Chicago, IL 60637, USA; EN)

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