This paper presents a synthesis of ent-alantrypinone (ent-6), the enantiomer of a natural product produced by the fungus Penicillium thymicola. The synthesis revolves around the Li[Me3AlSPh] -promoted isomerization of iminobenzoxazine 33 to quinazolinone 34, an N-acyliminium ion cyclization that converts enamide 9 to bridged indole 35, and rearrangement of 35 to oxindole ent-6, Ancillary chemistry that involves thermal fragmentation of an iminobenzoxazine to a nitrile ylide and Me2AlSPh-mediated cyclization of oxime ether-ester 22 to pyrrolidinone 23 is also described.