Chelate complexes with the P:O-double bond - a new concept for asymmetric synthesis.
A new strategy for asym. synthesis uses highly efficient cyclic P amidate auxiliaries capable of forming a rigid chelate complex with a metal enolate. The authors' research on asym. synthesis of ketone cyanohydrins is reviewed. Newly reported is the Pd(II)-catalyzed highly stereospecific rearrangement of olefinic cyanohydrin phosphates (e.g. 2-Ph-3-Me-3-Me-2-O-2-MeCH:CHCH(R)(CN)O-1,3,2-oxazaphospholidine) to phosphate protected g-hydroxy methacrylic nitriles (e.g. 2-Ph-3-Me-3-Me-2-O-2-NCC(R):CHCHMeO-1,3,2-oxazaphospholidine). Also, initial attempts at asym. N-methyl-a-amino acid synthesis are reported. For example, a high chem. yield of I with a de of 92% was obtained, but it was not possible to use higher homologous alkyl halides to alkylate alpha to the carbonyl C.
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