An Unusual Acyliminium Cyclization and Other Drawbacks during an Attempted Synthesis of a Chiral Primary α-Phosphinoalkanamine

Article abstract of DOI:10.1002/hlca.19980810506

Studies towards the synthesis of a chiral primary α-phosphinoalkanamine 1a are reported. O-Activated, N-carbamate-protected phenylalaninol 3a did not undergo 5_N reaction with KPPh₂: instead, after TV-deprotonalion, intramolecular substitution led to formation of the aziridine derivative 5a (Scheme 2). N-Phthalimido-protected. O-activated phenylalaninol 3b also underwent an intramolecular process on treatment with KPPh₂, i.e., an unusual aryl-acyliminium cyclization furnishing the (epoxymethano)isoindolo[1,2-a]isoquinolinone 7 (Scheme 3). In a reaction with KPPh₂, the N,N-dibenzyl-protected and activated phenylalaninol 3d finally yielded the intermolecular S_N reaction product 2a (Scheme 4). However, debenzylation by catalytic hydrogenation turned out to be impossible.