Rearranged lanostanes

The transformation of the lanostane keto-epoxide (72) into the cucurbitacin derivative (73) has been achieved with boron trifluoride in acetic anhydride. The presence of the acetic anhydride appears to favour the backbone rearrangement. The structure of (73) was confirmed by correlation with the oxidation product (74) of deoxybryogenin acetate. Two new cucurbitacin glycosides, arvenins 1 (75) and II (76) from Anagallis arvensis, have been reported. ... 

In the lanostane series, Lewis acids converted the 8a,9a-epoxide (422) into the 7,9(1 l)-diene (423), and the 9a, 1 la-epoxide (424) into a mixture of the 9)3,11-ketone (425) and the diene (426), resulting from a partial backbone rearrangement of a C(9)-carbonium ion. Although 9a,lla-epoxyandrost-4-ene-3,17-dione reacted with boron trifluoride to give only a modest yield of a 19(10— 9)aheo... 

The first successful transformation of a lanostane into a cucurbitane by a cationic process has been reported. On exposure to acid 3/3-acetoxy-9a-hydroxy-11-keto-5a-lanostane afforded two rearranged products (51) and (52) with a cucurbitane... 

Previous attempted syntheses of the cucurbitane skeleton from the lanostane skeleton by migration of the 19-methyI group have failed or resulted in low yields. An entry into the cucurbitane series via rearrangement of the epoxide from 3(3-acetoxylanostane-9,ll-ene-7-one has been reported (46 47). ° The... 

In connection with a synthesis directed towards the lanostane skeleton 204, Watt et al. used the Ireland-Claisen rearrangement of 202 as key step to introduce the quaternary center in 203 stereoselectively [118]. The diastereoselectivity of the... 

Despite the greather stability of the lanostane nucleus, it is apparently possible to reverse the protostane- lanostane rearrangement. It has been recently reported that the reaction of the epoxide (317) of dihydroparkeol acetate with Lewis acids affords, protostadienol acetate 318 (45%), presumably by secondary dehydration of protostene-3p,l la-diol... 

Levy, E. C., and D. Lavie Attempted Skeletal Rearrangements in the Lanostane Series. Israel J. Chem. 8, 677 (1970). 

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