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

Studies towards the synthesis of a chiral primary α‐phosphinoalkanamine 1a are reported. O‐Activated. N‐carbamate‐protected phenylalaninol 3a did not undergo SN reaction with KPPh2: instead, after N‐deprotonation, 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 SN reaction product 2a (Scheme 4). However, debenzylation by catalytic hydrogenation turned out to be impossible.