Biogenetic-Type Syntheses in the Rosane Series

[摘要] The diterpenoid mould metabolites, rosenonolactone (29) and deoxyrosenonolactone (46), have been synthesised from isocupressic acid (128) by a route patterned on their known biogenetic pathway. The key step in the proposed synthetic sequence, conversion of a bicyclic labdane to a tricyclic rosane, was first perfected on model labdadienols which lack the C-19 carboxyl group necessary for subsequent lactone formation. On brief acid treatment the labdadienols (70), (91), (92) and (93) were cyclised to pimaradienes (87) and (88). The mechanistic and stereochemical details of this cyclisation were investigated. Upon prolonged acid treatment the initially formed pimaradienes were converted to the desired rosadienes (111) and (112). Using the experience gained in the model series, isocupressic acid was similarly transformed into the acid (134) which had the correct C-4, C-8, C-9 and C-13 configurations required for a synthesis of the metabolites. The remaining problems of lactonisation, and, in the case of rosenonolactone, introduction of a C-7 carbonyl group, were jointly overcome by a method which employed the epoxide (149) as a key intermediate. Information on the hydrocarbon products resulting from acid rearrangement of the pimaradienes (87) and (88) was obtained from a combined gas chromatographic-mass spectral analysis using deuterated derivatives. No tetracyclic structures were detected and the principal product was shown to have the 'mixed' rosa-abietadiene skeleton (217).

[发布机构] University:University of Glasgow

[关键词] Organic chemistry