C -Alkylation of Functionally Substituted Carbanions with Cyclopropiminium Ions: A New Route to Cyclopropane Amino Acids

1-Diallylamino- and 1-dibenzylamino-1-cyclopropanols (3a,b) can easily be prepared in high yield from the corresponding secondary amines and cyclopropanone hemiacetal 1 (1-ethoxy-1-cyclopropanol). Their reactions with functionalized carbon nucleophiles such as ketene silyl acetals (1-methoxy-1-trimethylsiloxyethylene and methyl 3-methoxy-3-trimethylsiloxy-2-propenoate) and lithium enolates of alkyl esters under titanium(IV) chloride catalysis yield protected cyclopropane amino esters [1-aminocyclopropaneacetic acid derivatives]; subsequent deprotection to the free amino acids is also exemplified.