ORGANOTITANIUM-INDUCED STEREOSELECTIVE ALKYLATIVE ENDO-CLEAVAGE OF BENZYL PENTOPYRANOSIDES

The results presented are the first examples where organotitanium reag ents induced alkylative endo-cleavage of carbohydrates. The best condi tions for the alkylative transfer of a methyl group to benzyl 2-deoxy- 2- tert-butyldimethylsilyl)-alpha-D-arabinopyranoside (1) were the app lication of one equivalent of AlMe3 followed by four equivalents of Me TiCl3 generated by mixing TiCl4 and ZnMe2 in a ratio 2:1, or, alternat ively, treatment of 1 with two equivalents of 1:1 Me2TiCl2-ZnMe2. Both the yields and diastereoselectivities were comparable with those of t he reaction with AlMe3 but the titanium reagents were more reactive an d could be applied at much lower temperatures than the aluminium reage nt. (C) 1998 Elsevier Science Ltd. All rights reserved.