O-(2-Alkynyl) S-alkyl dithiocarbonates (allylic xanthates) were pyrolyzed to give 2-alkenyl alkyl sulfides (allylic sulfides) via the corresponding allylically isomeric S-(2-alkenyl) S-alkyl dithiocarbonates. The reaction follows the first-order rate law with relatively low sensitivity to the ionizing power of the medium and sizeably negative entropies of activation. When a mixture of two dithiol esters having different S-(2-alkenyl) groups and different S-alkyl groups was pyrolyzed, a "cross product" was not observed. The reaction was found to be facilitated by the presence of phenolic compounds or Lewis acids.Based on these findings together with modified neglect of diatomic overlap (MNDO) calculation data, the mechanism for the formation reaction of 2-alkenyl alkyl sulfides is discussed.
Deoxygenation of allylic alcohols to terminal olefins via stannylation/destannylation
作者:Yoshio Ueno、Hiroshi Sano、Makoto Okawara
DOI:10.1016/s0040-4039(00)77832-4
日期:1980.1
Deoxygenation of allylicalcohols to terminal olefins was performed via three steps; 1) [3,3]-sigmatropic rearrangement of O-allylxanthates, 2) the successive stannolysis with tributyltin hydride yielding allylic stannanes, and 3) final protolysis of allylic stannanes to terminal olefins.
Pyrolytic conversion of S-(2-alkenyl) S-alkyl dithiocarbonates (allylic dithiolcarbonates) to 2-alkenyl alkyl sulfides (allylic sulfides) was catalyzed by phenols bearing electron-attracting substituents. The reaction is pseudo-first-order and the apparent first-order rate constants are proportional not only to the concentration of phenols but also to the hydrogen-bonding capability of phenols. The entropy of activation for the phenol-catalyzed reaction is ca. 8 e.u. smaller than that for the uncatalyzed reaction. The reactivity of S-(1-phenylallyl) S-alkyl dithiocarbonates did not obey Hammett's or Taft's equation. Based on these findings together with the MNDO (modified neglect of diatomic overlap) calculation data, a possible role of phenols in the pyrolytic conversion of allylic dithiolcarbonates to allylic sulfides is discussed.
e with S-allyl S-methyl dithiocarbonate gave the endo cycloadduct whereas phencyclone gave a mixture of the endo and exo cycloadducts. The X-ray analysis of the cycloadduct of phencyclone and S-allyl S-methyl dithiocarbonate indicated the presence of a short contact of Ar–H···OC< type. A possible role of the interaction in determining the endo/exo selectivity was discussed based on the X-ray crystallographic