Novel Sesquiterpene Skeletons by Multiple Wagner–Meerwein Rearrangements of a Longipinane-1,9-diol Derivative

The tricyclic sesquiterpene (1R,3R,4S,5S,7S,8S,9S,10R,11R)-7,8-diangeloyloxylongipinan-1,9-diol, or rasteviol (7), underwent multiple Wagner–Meerwein molecular rearrangements and several hydride shifts when treated with Et2O–BF3 to generate the six new compounds (1R,3R,4S,5R,7S,8S,9S,10R,11S)-7,8-diangeloyloxy-1,9-epoxyjiquilpane (8), (1R,3R,4S,5R,7R,8S,9S,11S)-8-angeloyloxy-1,7-epoxyzamor-10(14)-ene (11), (2S,3R,4R,5R,6R,7R,8S,9S,10S)-7,8-diangeloyloxy-6,9-epoxyjanitziane (14), (4R,5R,7S,8S,9S,10S,11S)-7,8-diangeloyloxy-9-hydroxyjiquilp-3(15)-ene (16), (2S,3S,5R,7S,8R,10S,11R)-7,8-diangeloyloxyiratzian-9-one (18), and (2S,3S,5R,10S,11R)-8-angeloyloxyiratzi-7-en-9-one (22), of which 8, 11, 14, and 18 possess new hydrocarbon skeletons. Their structures were determined by 1D and 2D NMR in combination with single-crystal X-ray diffraction analyses of derivatives 10, 15, 20, and 21, which allowed confirmation of their absolute configurations by means of the Flack and Hooft parameters. In addition, some reacti...