An Access to 3,4‐(Aminomethano)proline in Racemic and Enantiomerically Pure Form

Protected racemic and enantiomerically pure 3,4‐(aminomethano)prolines rac ‐ 9 and (2 S ,2′ R ,3 R ,4 R )‐ 9 have been prepared applying a titanium‐mediated reductive cyclopropanation as a key step. Thus, cyclopropanations of N , N ‐dibenzylformamide with titanacyclopropanes generated in situ from racemic or enantiomerically pure tert ‐butyl N ‐Boc‐3,4‐dehydroprolinates rac ‐ 8 or ( S )‐ 8 proceed diastereoselectively, and furnish the protected racemic and enantiomerically pure diamino acid 9 . The latter was incorporated into three tripeptides containing glycyl, alanyl and phenylalanyl moieties.