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

Abstract

AbstractThe 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 CH2Cl2/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 (LiAlH4) 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 19F‐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 HXCH2CHR1R2, 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).