Glycopyranosyl trichloroacetimidates react with SmI2/O-2/THF to give 4-iodo-n-butyl 1,2-trans-glycopyranosides. Good to high yields can be obtained from 2 alpha-O-acylated trichloroacetimidates. With armed or manno substrates competitive formation of alpha-glycopyranosyl iodides occurs. (C) 1998 Elsevier Science Ltd. All rights reserved.