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.