4-(Phenylsulfonyl)-4-lithiocyclopentene as a nucleophilic 2-pentene-1,5-dial synthetic equivalent. An aziridine-based synthetic approach to (−)-alstonerine

Reaction of 4-lithio-4-(phenylsulfonyl)cyclopentene with an l-tryptophan-derived N-tosylaziridine provides an adduct. Oxidative cleavage of the cyclopentene double bond provides a dialdehyde, which enters into acid-catalysed Pictet–Spengler-type bicyclisation to give a tetracyclic aldehyde. Completely regioselective silyl dienol ether formation followed by completely stereoselective hetero-Diels–Alder reaction with monomeric formaldehyde gives a late-stage intermediate in a planned total synthesis of the macroline-related alkaloid (−)-alstonerine.