Application of the β-azidonation reaction to the synthesis of the antitumor alkaloid (+)-pancratistatin

Article abstract of DOI:10.1016/S0040-4020(98)00975-2

o-Vanillin 21 was converted into 24 following literature procedures. Treatment of 24 with n-BuLi/THF followed by addition of 25 gave 26. Dehydration (POCL₃/pyridine/DBU), hydrogenation and hydrolysis of 26 gave the ketone 29. Chirality was introduced by deprotonation of 29 with the lithium salt of (+)-bis(αmethylbenzyl)amine, followed by triisopropylsilyl trifluoromethanesulfonate to give 30 (95%). β-Azidonation of 30 with (PhiO)n/TMSN₃ rapidly produced 31 (95%) as a mixture of trans- and cis- diastereomers in a 3.5:1 ratio. Reduction with LiAIH4 followed by methyl chloroformate/pyridine gave 32, which on treatment with MCPBA/CH₂CL₂/imidazole resulted in 33. Hydrolysis of 33 gave 34, which when exposed to KOBu(t)/HMPA at 90 °C resulted in 39. After conversion of 39 into enone 42, epoxidation with NaHCO₃/H₂O₂/MeOH gave 43. Reduction of 43 with L-selectride followed by solvolysis with sodium benzoate in water gave 46, which was immediately acetylated to give 47. Lactam formation (Tf₂O/DMAP) converted 47 into 48 and the regioisomer 49 (7:1). The mixture of 48 and 49 demethylated to give 50 and the acetate protecting groups removed to give (+)pancratistatin 1.