8.9- Secofuranolactarane sesquiterpenes

The group of 8,9-secofuranosesquiterpenes so far comprises five compounds, two of which (19.1 and 19.2) were isolated from 

With respect to the aliphatic moiety (cyclopentene ring, plus protons at C-3, C-4, and C-12), 8,9-secofuranolactaranes gave NMR spectra resembling those of 8,9-seco-5-lactaranolide sesquiterpenes (Part 14) in addition, the two protons on the furan ring exhibited the characteristic couple of signals at 57.20-7.36. Remarkably, when a carbonyl group is attached to C-7, as in compounds 19.1 and 19.3, the signal of H-13 is shifted downfield to 57.95. 

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