Amino adds conformationally constrained

Hruby et al. used the rearrangement of cinnamyl ester 125g (entry 8) as a key step in their synthesis of conformationally constrained reverse turn dipeptide mimetics [67]. Piscopio et al. applied the rearrangement of crotyl esters in combination with an N-aUylation and subsequent ring dosing metathesis towards the synthesis of pipecoli-nic acid derivatives A [68], while Morimoto et al. used the rearrangement products for the synthesis of cyclopropyl amino adds B (Scheme 5.2.38) [69]. 

Whereas preparation of a-amino acid derivatives by asymmetric allylation of an acyclic iminoglycinate gave a modest enantioselectivity (62% ee) in an early investigation [189], the use of conformationally constrained nucleophiles in an analogous alkylation resulted in high selectivities (Scheme 8E.43) [190]. With 2-cyclohexenyl acetate, the alkylation of azlactones occurred with good diastereomeric ratios as well as excellent enantioselectivities. This method provides very facile access to a variety of a-alkylamino adds, which are difficult to synthesize by other methods. When a series of azlactones were alkylated with a prochiral gem-diacetate, excellent enantioselectivities were uniformly obtained for both the major and minor diasteieom-ers (Eq. 8E.20 and Table 8E.12). 

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