Base catalysed rearrangements involving ylide intermediates. Part 7. The rearrangements of allyl(pentadienyl)- and propynyl(pentadienyl)ammonium cations. The [5,4] sigmatropic rearrangement
作者:Trevor Laird、W. David Ollis、Ian O. Sutherland
DOI:10.1039/p19800002033
日期:——
The basecatalysedrearrangements of the cations (7), (17), (22), and (27) gave the enamines (9), (18), (23), and (28), which on hydrolysis yielded the aldehydes (10), (19), (24), and (29) respectively. The reactions are shown to be concerted [5,4] sigmatropic rearrangements proceeding via a nine-membered transition state involving 10π electrons. The basecatalysedrearrangements of the 3-phenylprop-2-ynyl
Dynamic NMR Study of the Rotation around “Biphenyl-Type” Bonds in Polycyclic Sulfoxides
作者:Samuel Braverman、Yossi Zafrani、Hugo E. Gottlieb
DOI:10.1021/jo010947z
日期:2002.5.1
on the synthesis and the products of both symmetrical and asymmetrical starting materials. We also measure, by NMR techniques, the rotation rate of the side chain for several such polycyclic sulfoxides. The barriers for this process, which is similar to a biphenyl rotation, are very strongly dependent on the nature of the substrate, ranging between <7 and 21.0 kcal.mol(-1) for sulfoxides with two five-membered
Visible light initiates the stereoselective formation of two new bonds, a CC and a CSi bond, during the addition of acylsilanes to alkynes. At room temperature this photochemicallyinduced transformation can be applied for the preparation of chromone derivatives in a highly atom-economic manner.
Oxydation d'alcools ω-vinylalléniques par l'hydroperoxyde de tertiobutyle
作者:Alain Doutheau、Jacques Gore、Joseph Diab
DOI:10.1016/s0040-4020(01)96424-5
日期:1985.1
The oxidation of α-vinylallenic alcohols 3 with t-butylhydroperoxide in the presence of catalytic amounts of vanadyl acetylacetonate, yields the epoxides 6 or, mainly, the cyclopentenones 5 depending on the secondary or tertiary class of the alcoholic function. In the same conditions, the vinylallenic alcohols 4 lead only to cyclopentenones 7.
Base catalyzed rearrangement of π-conjugated sulfur and selenium bridged propargylic systems
作者:Samuel Braverman、Yossi Zafrani、Hugo E Gottlieb
DOI:10.1016/s0040-4020(01)00923-1
日期:2001.10
A series of novel π-conjugated bis-propargylic sulfides, selenides, sulfoxides and sulfones have been prepared. In the presence of amine bases these compounds underwent facile isomerization to the corresponding allenes, followed by a tandem cyclization and aromatization of the latter via a diradical intermediate. While the reactions of sulfones and sulfoxides were almost spontaneous and proceeded in