Nonreductive Enantioselective Ring Opening of N ‐(Methylsulfonyl)dicarboximides with Diisopropoxytitanium α,α,α′,α′‐Tetraaryl‐1,3‐dioxolane‐4,5‐dimethanolate

The bicyclic and tricyclic meso‐N ‐(methylsulfonyl)dicarboximides 1a–f are converted enantioselectively to isopropyl [(sulfonamido)carbonyl]‐carboxylates 2a–f by diisopropoxytitanium TADDOLate (75–92% yield; see Scheme 3 ). The enantiomer ratios of the products are between 86:14 and 97:3, and recrystallization from CH 2 Cl 2 /hexane leads to enantiomerically pure sulfonamido esters 2 ( Scheme 3 ). The enantioselectivity shows a linear relationship with the enantiomer excess of the TADDOL employed ( Fig.3 ). Reduction of the ester and carboxamide groups (LiAlH 4 ) and additional reductive cleavage of the sulfonamido group ( Red‐Al ) in the products 2 of imide‐ring opening gives hydroxy‐sulfonamides 3 and amino alcohols 4 , respectively ( Scheme 4 ). The absolute configuration of the sulfonamido esters 2 is determined by chemical correlation (with 2a,b ; Scheme 6 ), by the X‐ray analysis of the camphanate of 3e ( Fig. 1 ), and by comparative 19 F‐NMR analysis of the Mosher esters of the hydroxy‐sulfonamides 3 ( Table 1 ). A general proposal for the assignment of the absolute configuration of primary alcohols and amines of Formula HXCH 2 CHR 1 R 2 , X = O, NH, is suggested (see 11 in Table 1 ). It follows from the assignment of configuration of 2 that the Re carbonyl group of the original imide 1 is converted to an isopropyl ester group. This result is compatible with a rule previously put forward for the stereochemical course of reactions involving titanium TADDOLate activated chelating electrophiles ( 12 in Scheme 7 ). A tentative mechanistic model is proposed ( 13 and 14 in Scheme 7 ).