NONREDUCTIVE ENANTIOSELECTIVE RING-OPENING OF N-(METHYLSULFONYL)DICARBOXIMIDES WITH ',ALPHA'-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 an d 97:3, and recrystallization from CH2Cl2/hexane leads to enantiomeric ally pure sulfonamido esters 2 (Scheme 3). The enantioselectivity show s a linear relationship with the enantiomer excess of the TADDOL emplo yed (Fig. 3). Reduction of the ester and carboxamide groups (LiAlH4) a nd 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 (wit h 2a,b; Scheme 6), by the X-ray analysis of the camphanate of 3e (Fig. 1), and by comparative F-19-NMR analysis of the Mosher esters of the hydroxy-sulfonamides 3 (Table 1). A general proposal for the assignmen t of the absolute configuration of primary alcohols and amines of Form ula 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 carbony l group of the original imide 1 is converted to an isopropyl ester gro up. This result is compatible with a rule previously put forward for t he stereochemical course of reactions involving titanium TADDOLate act ivated chelating electrophiles (12 in Scheme 7). A tentative mechanist ic model is proposed (13 and 14 in Scheme 7).