A synthetic approach to the quassinoids

Triterpenoids

“…Dukunolide A (1 30) (from Lansium domesticum), for which the structure was established by X-ray analysis,93 may arise from a bicyclononanolide intermediate by cleavage of the C-9-C-10 bond followed by formation of a bond between C-1 and C-14. Cleavage of the C-9-C-10 bond is certainly involved in the biogenesis of carapolides A (131), B (132), and C (133) (from the seeds of Carapa p r o~e r a~~) and carapolides D (134) and E (135) (from the seeds of C. grand@orag5). The spirolactone carapolide F (136) (from C .…”

“…g r a n d f l~r a~~) is an attractive precursor of this group. A retro-Prins reaction leads to the methyl ketone carapolide B (132), which can undergo vinylogous 0-dicarbonyl cleavage to give the hexanortri terpenoid carapolide A (131). (145) and (146) The modified furan derivative compositolide (salannolide) (160) has been isolated both from Melia dubia106 and Azadirachta indica.…”

Synthesis of 3, 4, 4a, 5, 6, 7, 8, 8a α-Octahydro-4a β, 8α-Dimethyl-2(1H)-Naphthalenones from the Wieland-Miescher Ketone

“…Among the numerous Diels Alder .approaches2 to the picrasane skeleton 2 of the quassinoids, the reaction of a bicyclic AB ring dienophile 1 with a suitable diene has emerged as a successful ~p t i o n .~ to develop an enantioselective route to the quassinoids, we converted the Wieland-Miescher ketone ( 4 1 , which is available in 98% ee, to bicyclic dienophiles 6 Finding that the late introduction of the C-4 picrasane methyl group was problematical, we developed an alternative approach for introducing the C-4 methyl group early in the synthetic route.…”

“…In seeking The preparation of either the C -1 methoxy or C -1 tert-butyldimethysilyloxy-substituted dienophiles 6 and of 30% H 0 in four portions over 10 min intervals. The prod&$ was diluted with H 0, extracted with CHC13, washed with saturated NaHC03 sglution and brine, and dried over MgS04.…”

“…3,4,4a,5,6,7-Hexahydro-5~-tert-butyldimeth~lsil~l-solution, and concentrated to af ord 1. (CDC1 ) 6 0.04 and 0.05 (two s,6, Si(CH ) 1, 0.91 ( s ,9, i!iC(CH 1, 1.00 ( s , 3, C-4aP CH ),32?02 (s, 3, OCOCH3), 3.3 ?dd, J=4 and 12 Hz, 1, CAOTBS) , 5.25-5.38 (m, 1, C-8 HI, 5.67 (d, J=2 Hz, 1, C-1 H); exact MS calcd for C H 0 Si 336.2122, found 336.2120. 4,4a, 5,6,7,8-Heft~h$~r&5P-tert-butyldimethylsilyloxy-8-hydroxy-4a~-methyl-2(3H~-napthalenone (21).…”