Abstract:Eleven new substances related to the proposed mechanistic pathway
from longipinane 2 to
arteagane
(2,6,6,11-tetramethyltricyclo[5.4.0.04,8]undecane)
derivatives were prepared and are
discussed.
“…This has been used to generate compounds with novel hydrocarbon skeletons. In most cases, the rearrangements have involved the seven-membered ring − and, more recently, the six-membered ring . To accomplish the latter, the carbonyl group at C-1 was reduced to a hydroxyl group, which is adjacent to the four-membered ring.…”
The molecular rearrangement of (1R,3S,4S,5S,7S,8R,9S,10R,11R)-7,8,9-triacetyloxylongipinan-1-ol (4) under acidic conditions afforded (1S,4R,5R,7S,8R,9S,10S)-7,8,9-triacetyloxyuruap-3(12)-ene (5), while 6, the C(3)-stereoisomer of 4, after two consecutive Wagner-Meerwein rearrangements followed by two 1,2-hydride migrations, afforded (4R,5R,7S,8S,9S,10S,11S)-7,8,9-triacetyloxyjiquilp-3(12)-ene (7), which possesses a new hydrocarbon skeleton. The structures of the new substances were elucidated by 1D and 2D NMR data in combination with X-ray diffraction analyses of the uruapane, longipinane, and jiquilpane derivatives 5, 6, and 14, respectively. Molecular modeling at the ab initio level was used to study the reaction mechanisms, while deuterium labeling was employed to confirm the C-C bond migrations and the hydride shifts.
“…This has been used to generate compounds with novel hydrocarbon skeletons. In most cases, the rearrangements have involved the seven-membered ring − and, more recently, the six-membered ring . To accomplish the latter, the carbonyl group at C-1 was reduced to a hydroxyl group, which is adjacent to the four-membered ring.…”
The molecular rearrangement of (1R,3S,4S,5S,7S,8R,9S,10R,11R)-7,8,9-triacetyloxylongipinan-1-ol (4) under acidic conditions afforded (1S,4R,5R,7S,8R,9S,10S)-7,8,9-triacetyloxyuruap-3(12)-ene (5), while 6, the C(3)-stereoisomer of 4, after two consecutive Wagner-Meerwein rearrangements followed by two 1,2-hydride migrations, afforded (4R,5R,7S,8S,9S,10S,11S)-7,8,9-triacetyloxyjiquilp-3(12)-ene (7), which possesses a new hydrocarbon skeleton. The structures of the new substances were elucidated by 1D and 2D NMR data in combination with X-ray diffraction analyses of the uruapane, longipinane, and jiquilpane derivatives 5, 6, and 14, respectively. Molecular modeling at the ab initio level was used to study the reaction mechanisms, while deuterium labeling was employed to confirm the C-C bond migrations and the hydride shifts.
“…The individual 1 H and 13 C NMR assignment of Me-12 and Me-13 was established by NOESY correlations from Me-12 to H-4 and from Me-13 to H-11, together with a HETCOR spectrum. In those cases where the NOESY experiments did not allow such proton assignments, due to their chemical shift proximity, they were followed by inspection of the HETCOR data taking into account the 13 C assignments determined by analogy with the whole series of new and previously reported derivatives. − , …”
Section: Resultsmentioning
confidence: 99%
“…Several highly functionalized longipinene derivatives are found as the main constituents of many species of the genus Stevia . These classes of substances, whose absolute configuration is known, have shown an important tendency to undergo molecular rearrangements due to the strained fused cyclobutane located between a six- and a seven-membered ring. − These naturally occurring sesquiterpenoids are generally functionalized at C-1 with a carbonyl group and at C-7, C-8, C-9, and C-13 with hydroxyl and/or acyloxy groups…”
Ultraviolet irradiation of (1R,3S,4S,5S,10R,11R)-1-acetyloxy-7-oxolongipin-8-ene (6), prepared from longipinene diesters isolated from Stevia salicifolia, afforded the new quirogane (7) and prenopsane (8) derivatives, as the major products, together with the minor secondary photoproduct (1R,3R,5R,8S,11S)-1-acetyloxy-7-oxopatzcuar-9-ene (9), which possesses a novel tricyclic sesquiterpene skeleton. The stereostructures of the new compounds 7-9 were mainly determined by NMR techniques including COSY, HSQC, HMBC, and NOESY in combination with molecular modeling obtained by density functional theory calculations. A reaction mechanism accounting for the observed transformations is proposed.
“…160 Other sesquiterpenes with this carbon framework -longipin-2-en-3-one 119 and 12-hydroxy--longipinene 120 have been isolated from Achillea millefolium 161 and Juniperus chinensis, 107,108 respectively. The acid rearrangement of longipinane into arteaganane has been studied, 162 whilst the photochemical rearrangement of a longipinane derivative into a vulgarone derivative and a compound with a new tricyclic skeleton, has been investigated. 163 The structure of isoculmorin has been determined as 121 by X-ray analysis.…”
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