Asymmetric Syntheses via Heterocyclic Intermediates, XXVII. Reactions of Metallated Bislactim Ethers of cyclo(‐L‐Val‐Gly‐) with ( R )‐ and ( S )‐Glyceraldehyde and with ( S )‐Lactaldehyde

The titanium derivative 3 and the lithium derivative 2 of the bislactim ether 1 of cyclo(‐L‐Val‐Gly‐) react with ( R )‐ and ( S )‐glyceraldehyde (cyclohexylidene‐protected, 9 ) and with ( S )‐lactaldehyde (Mem‐protected, 10 ) to give virtually only one diastereomer. The extent of asymmetric induction is higher for ( S )‐ 9 and 10 than for ( R )‐ 9 . The results can be rationalized on the basis of pericyclic reactions with six‐membered chair‐like transition states. – On acid hydrolysis (subsequent to O ‐acetylation) the aldol‐type addtion products 11 , 12 , and 13 are cleaved to give the amino acid methyl esters 14 , 15 , and 16 with multiple stereocenters. 15 and 16 are enantiomerically and diastereomerically pure.