Expeditious syntheses of (+/-)-5-oxosilphiperfol-6-ene and (+/-)-silphiperfol-6-ene

[reaction: see text]Stereocontrolled syntheses of 5-oxosilphiperfol-6-ene (1) and silphiperfol-6-ene (2) have been accomplished in four and five steps, with overall yields of 32% and 26%, respectively, from 1-acetyl-3-methylcylopentene. The strategy features two pivotal reactions: (a) a Diels-Alder reaction between 1,3-dimethylcyclopentadiene and 1-acetyl-3-methylcyclopentene, which proceeds with remarkable regio-, endo-, and diastereofacial selectivities, and (b) an intramolecular Paterno-Büchi reaction to snap together the triquinane framework.