6-epi-a-Santonin

Deoxygenation. Greene has applied Kabalka s method for reduction of an enone (6, 98 7, 54) to the tosylhydrazone of a cross-conjugated ketone, 6-epi-a-santonin (2). Unexpectedly only one olefin (3) was obtained in 50% yield. This product was converted into the diene 4 by allylic oxidation, reduction to an allylic alcohol, and dehydration. The product was converted into (—)-dictyolene (5) by a method developed previously. ... 

FIGURE 20.64 Biotransformation of 6-epi-a-santonin (190) by Absidia coendea. Asparagus officinalis, Marchantia polymorpha, and Nicotiana tabacum. 

Epi-a-santonin in aq. 45%-acetic acid irradiated under reflux in a N2-atmos-phere until the rotation has reached 74 6-epi-zsop/iofo-a-santonic lactone. Y 24%. F. e. s. D. H. R. Barton, J. E. D. Levisalles, and J. T. Pinhey, Soc. 1962, 3472. 

H,gOg, 1,10 2,3-Diepoxy-6,8-dihydroxygermacr-4-ene-12,15-dioic acid di-7-lactone, 40B, 507 5H17Br03, 2-Bromo-(-)-a-desmotroposantonin, 43B, 691 2-Bromo-(-)-j3-desmotroposantonin, 32B, 249 2-Bromo-a-santonin, 30B, 226 2-Bromo-/3-santonin, 34B, 309 2-Bromo-6-epi-a-santonin, 41B, 621 2-Bromo-6-epi-j3-santonin, 41B, 621... 

Frullanolide (338), with a d s-lactone ring, has been isolated from the epiphytic liverwort, Frullania tamarisci. The structure was deduced from its spectral properties (775,255, 287) and confirmed by conversion to l,2-dihydro-6-epi-P-santonin (366) also obtained from 6-epi-P-santonin (367) (775, 287) (Scheme 40). The enantiomer (339) of (338) was isolated from European F, dilatata (30, 175, 287). 

The a-methylene-) -butyrolactone grouping is incorporated in a large number of sesquiterpenoids, many of which have significant biological activity. A number of routes have been devised for the synthesis of this moiety but recently an important contribution from Ourisson s laboratory has demonstrated that the more accessible a-methyl-y-lactones can be converted in two steps into the a-methylene analogues.This is achieved by reaction of the lactone (263 R = H) with triphenylmethyl-lithium and quenching the resultant enolate with 1,2-dibromoethane. Dehydrobromination of the derived bromide (263 R = Br) with diazabicyclononene gives exclusively the exocyclic methylene lactone (264). This method is only suitable for c/s-y-lactones since the trans-lactone yields exclusively the endocyclic isomer. To illustrate this method Ourisson et at. have converted dihydro-6-epi-santonin (265) into (- )-frullanolide (266). More recently the same authors have developed a method which is applicable to... 

Making use of their recently developed photochemical decarboxylation of cis-fused y-lactones (diffuse Strasbourg sunlight), Ourisson et have converted the keto-lactone (316), derived from dihydro-6-epi-santonin, into-epi-maalienone (317). Further irradiation of (317) resulted in the formation of a-cyperene (318) and /J-cyperene (319). 

Asparagus officinalis also biotransformed a santonin (190) into three eudesmanolides (187,207, 208) and a guaianolide (209) in a small amount. 6 epi Santonin (198) was also treated in the same bioreactor as mentioned earlier to give 199 and 206, the latter of which was obtained as a major metabolite (44.7%) (Yang et al., 2003) (Figure 20.63). 

Frullanolide (338) was synthesized from a-santonin (368) by the reactions shown in Scheme 40 (130—132). Dihydrofrullanolide (341) was obtained from l,2-dihydro-6-epi-santonin (370) in 40% overall yield by five... 

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