Mechanisticstudies of the photochemicalrearrangement of 1-oxolongipin-2-ene derivatives

Ultraviolet irradiation of (4R,5S,7S,8R,9S,10R,11R)-7,8,9-triacetyloxy-1-oxolongipin-2-ene (2) afforded the vulgarone A 7 and the pingilonene 8 derivatives as the major products, which were formed by a [1,3]-shift, together with the minor secondary photoproducts 9 and 10. The phototransformation mechanism is discussed in terms of individual ultraviolet irradiation of 7 and 8 in combination with the monitoring reaction progress of 2 by 1H NMR measurements. The stereostructures of the new carbocyclic skeleta were geometry optimized using density functional calculations.