Abstract Hetero Diels-Alder reaction of diene 7, obtained in four steps from aldehyde 4, with Troc-NO 8 produced the dihydro-2H-1,2-oxazine 9 in 48% yield. Conversion of this intermediate to the N-deprotected tosylate 10 followed by ring closure gave the bicyclic product 11 which was converted to the indolizidine derivative 13 by N‒O bond cleavage (H2, RaNi) and recyclization under Mitsunobu conditions. Final deprotection of 13 with mild acid gave the target triepicastanospermine analog 3.