The Rearrangement of α‐Acetylenic Alcohols to α, β‐Unsaturated Carbonyl Compounds by Silylvanadate Catalysts

Abstract

Summary. New catalytic systems have been found which effect the isomerization of ccacetylenic alcohols to the corresponding a,P-unsaturated carbonyl compounds with high efficiency. These are combinations of silylvanadates with silanols or silanediols.u,p-Unsaturated carbonyl compounds, important intermediates in the manufacture of fragrances [l], carotenoids, and vitamins [Z] [6] and some contradictory reports [7]. Such rearrangements have been achieved by the use of a wide variety of acidic reagents [5] [6] [8] which often lead to complex mixtures of products. Meyer-Schuster RupsRearrangements of esterified acetylenic alcohols, however, proceed in high yield in the presence of certain transition metals [9] in charge induced [3s, 3s]-sigmatropic reactions [ l O j [ll], and the intermediates saponify cleanly to cr,P-unsaturated carbonyl compounds. Such a reaction has provided an important technical process for the manufacture of citral (2 $-3) from dehydrolinalool (1).

Atom transfer and rearrangement reactions catalyzed by methyltrioxorhenium, MTO

“…This delay is the result of a long induction period, often 2-4 days, more than an inherently slow process. Once that time had elapsed, product buildup occurred usually within [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] hours and could be observed in the IH NMR spectra. Further NMR studies were carried out for 1-phenyl-2-prop yne-l-ol, entry …”

“…These alcohols afford rearrangement products, a,p-unsaturated carbonyl compound^.^^ They are valuable intermediates in organic synthesis, finding application for fragrances, carotenoids, etczO Certain transition metal complexes are known to mediate the isomerization of propargylic alcohols by a 1,3 transposition of oxygen, as given in eq 1, referred to as a Meyer-Schuster rearrangement, [21][22][23][24][25] or by hydride migration, a Rupe rearrangement. 21,[26][27][28][29] Owing to the potential synthetic economy of such isomerizations, both of these rearrangements have been the focus of prior effort, as cited previously.…”

Tris(triphenylsiloxy)vanadium Oxide

“…2 It is thought that the formation of the initial vanadate ester from the reaction of 1 and propargylic alcohol is the rate-determining step, as evidenced by (1) faster rearrangements when there are electron-deficient aryl groups on the siloxy ligand and (2) presence of excess triphenylsilanol. 1 In the example shown below, the addition of a small amount of carboxylic acid proved to be useful in achieving the complete conversion. While linear propargylic alcohols generate α,β-unsaturated carbonyl compounds, cyclohexanol derivatives generally give a mixture of α,β-and β,γ-unsaturated carbonyl compounds under similar conditions (eq 2).…”

Rearrangements involving allenes

“…431. The key step is believed to be a [3,3] the vanadate ester 741, which is formed initially by a transesterification reaction.…”