Conjugate Additions of 1-Propenylphosphonates to Metalated Schöllkopf's Bis-lactim Ether: Stereocontrolled Access to 2-Amino-3-methyl-4-phosphonobutanoic Acids
Diastereoselectivity in the conjugateaddition of metalated Schöllkopf's bis-lactim ethers 5a-e to (E)- and (Z)-1-propenylphosphonates 4a,b was studied experimentally and theoretically and utilized to achieve a direct and stereocontrolled synthesis of all four diastereoisomers of 2-amino-3-methyl-4-phosphonobutanoic acid, 6a,b and their enantiomers. The relative stereochemistry was assigned from an