Stereoselective synthesis of pinane-based β- and γ-amino acids via conjugate addition of lithium amides and nitromethane

Michael addition of dibenzylamine to (?)- and (+)-tert-butyl myrtenate, (?)-2 and (+)-2, derived from (?)- and (+)-myrtenal, furnished monoterpene-based β-amino acid derivatives in highly stereospecific reactions. The resultant amino esters (?)-3 and (+)-3 were transformed to unsubstituted, mono- and disubstituted and Fmoc-protected amino acids (?)-6-11 and (+)-6-11, which are promising building blocks for the synthesis of β-peptides and 1,3-heterocycles. The microwave-assisted conjugate addition of nitromethane to α,β-unsaturated esters (?)-12 and (+)-12 likewise resulted in nitro esters (?)-13 and (+)-13 in highly stereospecific reactions. Compounds (?)-13 and (+)-13 were successfully transformed into γ-amino acids (?)-16 and (+)-16 in two steps.