Hirsutic acid, rearrangement

The p-bromophenylacyl ester of hirsutic acid (36, Scheme 24) shows a dramatic topotactic rearrangement induced by the x-ray irradiation [72]. The reactant lattice is preserved in the conversion of 36 to a 2 3 ratio of 36 and its keto form, 37. 

Hirsutic acid C has been observed to rearrange to a biologically active isomer called hirsutic acid N or isohirsutic acid which has been formulated as 348. A convergent, stereocontrolled sythesis of this molecule has also been described by Lans-bury (Scheme 54).336) Claisen alkylation of 342 with 345 again proved to be site-... 

Ethyl diazoacetate has been used extensively in the homologation of ketones to 3-keto esters. Lewis acid is required for the reaction (equation 23). ° There is a tendency for the least-substituted group to migrate, particularly if one group is fully substituted (equation 24). In a total synthesis of ( )-aplysin (20) this selective rearrangement was applied (Scheme 9), and a similar approach was used in a synthesis of (+)-hirsutic acid. Ethyl diazoacetate has also been used in the homologation of acyclic... 

The hirsutane carbon skeleton, which is found in some other antibiotics produced by the Basidiomycetes, is also formed by a sequence of Wagner-Meerwein rearrangements of a protoilludane carbocation via 5.58. Hirsutic acid... 

Last year Lansbury and co-workers reported the first synthetic approaches to the fungal metabolite hirsutic acid C (196). They have now taken one of their previous intermediates (197) through to isohirsutic acid (201), which is a rearrangement product of hirsutic acid Thus, Claisen alkylation of (197) with the alcohol (198) gave (199) together with the epimer at C-7. Treatment of (199) with 90% sulphuric acid effected a number of transformations (i) vinyl chloride hydrolysis, (ii) )3-thioI elimination, and (iii) ester hydrolysis to generate (200),... 

Photoinduced epimerization reactions are sometimes encountered during the course of the ODPM rearrangement. Thus, it has been observed, as part of a study directed toward the total synthesis of (+)-hirsutic acid and (-)-complicatic acid, that triplet-sensitized irradiation of compound 97 affords the anticipated primary photolysis product 98, but this is accompanied by quantities of epimer 99. Sustained irradiation leads to increasing quantities of the thermodynamically favored isomer 99, presumably via either photoenolization of precursor 98 or through photoinduced C—C bond homolysis within the same compound followed by diradical recombination (to generate 99). 

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