Conversions of .alpha.-methyl to .alpha.-methylene-.gamma.-lactones. Synthesis of two allergenic sesquiterpene lactones. (-)-Frullanolide and (+)-arbusculine B

New advances in the volatile metabolites of Frullania tamarisci

“…Finally, the 36 has been unambiguously assigned to γ‐dihydrocyclocostunolide (Figure B ‐ insert); in addition, the new structure has been also supported by the perfect agreement between its spectral data and those recorded for the main product obtained by NaBH 4 reduction of the CC‐F7 (γ‐cyclocostunolide, 37 , 27.0%). A similar structure has been reported by Barton et al and Greene et al as a reaction intermediate of Raney nickel desulphurisation of ethylenethioacetal of 1,2‐dihydrosantorin. Since the knowledge of the chemical constituents of liverworts might serve to define not only chemical, but also evolutionary relationships within Marchantiophyta, γ‐dihydrocyclocostunolide, a natural product never described previously, can be used as taxonomic indicator.…”

Synthesis of yomogin, 1-deoxyivangustin, and 1-deoxy-8-epiivangustin

“…After refluxing under 83%), homogeneous by tlc, whichwas shownby nrnrto containasmall Ar for 15 min, the reaction mixture was cooled to room temperature, percentage (ca. 5%) of a double-bond isomer, probably the ~3 -i~ treated with excess of ethereal diazomethane, filtered, concentrated (16). Elimination of this minor impurity took place in the chromatoin vacuo7 and chromatographed on silica gel.…”

“…The overall yield of 11 from 1 was thus 33-35% (Scheme 1). Since epimerization at C-6 of 1,2-dihydro-a-santonin takes place with much better yields (16) than that of a-santonin, we also examined this alternative. Lactone 11 was obtained via 1,2-dihydroartemisin 8 in an overall yield of 58-60% from 1.…”

“…By reaction with ethanedithiol, 11 gave the thioketal 12, which yielded, by treatment with active Raney nickel, the unsaturated lactone 13 (17), contaminated with a small percentage (ca. 5%) of a double-bond isomer (16). Phenylselenylation and subsequent oxidation afforded 4 in an overall yield of ca.…”

Utilization of trimethylsilylpropyne as an acetonyl unit in the synthesis of cyclopentenones. Applications to the synthesis of jasmone and dihydrojasmone

“…This is consistent with the several other reports of bromine transfer in the reaction of P-substituted bromoalkanes and reactive nucleophiles (see for example ref. 8). However, we were able to prepare the desired 1,4-diketones 6 using 3-bromo-1-trimethylsilyl-1-propyne (9) as outlined in Scheme 1.…”