Lanostane to cucurbitane transformations

Edwards, O. E.; Kolt, R. J.

doi:10.1139/v87-104

Cited by 8 publications

(1 citation statement)

References 16 publications

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“…The cucurbitacins are biogenetically derived from 2,3oxidosqualene via 10-cucurbita-5,24-dien-3-ol (cucurbitadienol) as the crucial intermediate (Shibuya et al, 2004). In chemical synthesis, the cucurbitane derivatives are available from the reaction of 9-substituted lanostane derivatives via C-9 carbocationic intermediates (Paryzek, 1976(Paryzek, , 1979Edwards & Paryzek, 1983;Edwards & Kolt, 1987).…”

Section: Commentmentioning

confidence: 99%

Two isomeric cucurbitane derivatives

2009

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Two isomeric cucurbitane derivatives, 3beta,7alpha,11beta-triacetoxycucurbit-5(10)-ene, (I), and 3beta,7alpha,11beta-triacetoxy-5alpha-cucurbit-1(10)-ene, (II), both C(36)H(58)O(6), have their single endocyclic C=C double bonds in different positions. This results in differences in the conformation of the four-ring system, which is close to a half-chair/half-chair/chair/half-chair arrangement in (I) and to a half-chair/twist-boat/boat/half-chair arrangement in (II). The orientation of some of the substituents is also different; the 3beta-acetoxy group is in an equatorial position in (I) but in an axial position in (II), while the 11beta-acetoxy group occupies an axial position in (I) and an equatorial position in (II). The asymmetric unit of (I) contains two symmetry-independent molecules which do not differ significantly, being related by a pseudo-twofold axis of symmetry. In both structures, the aliphatic chain fragments are disordered and the disorder persists at lower temperatures.

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Section: Commentmentioning

confidence: 99%

Two isomeric cucurbitane derivatives

2009

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Westphalen Rearrangement

2010

Comprehensive Organic Name Reactions and Reagents

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This rearrangement is an acid‐promoted Wagner–Meerwein rearrangement of 5‐hydroxycholesterol derivatives with a substituent at C‐6 in β‐configuration, from which the 5‐hydroxy is removed by acidic dehydration accompanying the migration of the angular methyl group at C‐10 to C‐5 and the formation of double bond between C‐9 and C‐10 and this transformation is generally referred to as the Westphalen rearrangement. It has been reported that the rearranged compound by means of the treatment of cholestane‐3β,5α,6β‐triol 3,6‐diacetate with sulfuric acid and acetic anhydride is referred to as the Westphalen's diol diacetate and is quite general among the steroids. The study finds that depending on the substituents around C‐5 and C‐6, the Westphalen rearrangement can be initiated by different reagents. However, it has been noticed that only those steroids having a substituent at C‐6 with a β‐configuration can undergo the Westphalen rearrangement. The initial protocol used by Westphalen has been improved by the use of potassium bisulfate. This rearrangement is quite often for steroids with 6β‐groups and 5α‐OH, or a 5α,6α‐ epoxide ring, which has been used for the structural transformation among the steroids.

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