Convergent Synthesis of Pancratistatin from Piperonal and Xylose

A synthesis of the antitumour agent pancratistatin is described from piperonal and D-xylose. Piperonal is converted into cinnamyl bromide 11 while methyl 5-iodoribofuranoside 12 is derived from xylose. The allylic bromide and the iodocarbohydrate are combined in a zinc-mediated tandem reaction to afford a highly functionalised 1,7-diene, which is then converted into the corresponding cyclohexene by ring-closing olefin metathesis. Subsequent Overman rearrangement, dihydroxylation and deprotection afford the natural product in a total of 25 steps from the two starting materials. The longest linear sequence is from piperonal and gives rise to pancratistatin in 18 steps and 7.0% overall yield. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)