Ethylene derivs bond migration

The double bond migration which normally occurs on forming ethylene ketals from A -3-ketones has frequently been utilized to form derivatives of the A -system. The related transformation of A -3-ketones into A -3-alcohols is usually accomplished by treatment of the enol acetate (171) (X = OAc) with borohydride. This sequence apparently depends on reduction of the intermediate (172) taking place faster than conjugation ... 

Sodium trihydridocyanoborate hydrochloric acid Ethylene derivs. from a,j -ethylenetosylhydrazones with double bond migration... 

Ethylene derivs. from 2-ethylenestannanes with migration of the carbon-carbon bond... 

Synthesis of ethylene derivatives from 1,3-dienes with migration of a carbon-carbon double bond... 

Ethylene derivatives from acetoxy compounds Partial formation with and without migration of a bond s. 11, 927 GHG(OAc) - G G carbon-carbon double... 

An example of the photodecomposition of a dithiin to give a stable dithiet, with elimination of ethylene, has been reported.206 A different reaction is preferred in the dithiins (261), which on irradiation, are converted to benzene derivatives (262) via the 1,4-dithiocins (263).207 The cyclic trimer of thio-acetophenone on irradiation in cyclohexane yields thioacetophenone.208 An initial carbon-sulfur bond homolysis is also responsible for the conversion, on irradiation in methanol, of a 3-cephem to two thiazoles,209 whereas a 1,2-alkyl migration followed by a further photochemically induced carbon-sulfur bond homolysis has been proposed to account for the photorearrangement of the sulfonium ylides (264) to the pyrimido-l,4-benzo[h]thiazepines (265).210 The novel photorearrangemenl of a 1,3-thiazine to a cyclopro-pathiazolidine has also been rationalized in terms of an initial carbon-sulfur... 

The reaction is proposed to proceed via a two-step sequence (i) catalytic car-bonylation of the olefinic C-H bond of a,/i-unsaturated imines after insertion of ethylene and (ii) intramolecular nucleophilic attack of the imine nitrogen on the ketonic carbon followed by a 1,2-ethyl migration (Scheme 7.13). The initial formation of ethyl ketone was confirmed by the reaction of a cyclic unsaturated imine, which produced a -aminocyclopentene derivative via an aldol-type condensation of the initially formed ketone (Eq. (7.54)). 

IJydrogenation of the A -bond in an alkaline medium was accompanied by the migration of the A -bond into the A -position and gave the 5i3-diketone (45), the further hydrogenation of which yielded the 8a, 9j3-derivative (17) (see Scheme 57). The conversion of (45) into the 3-ethylene-dioxy-13-hydroxymethylene derivative (44) and subsequent alkylation with methyl iodide and bromoacetate led after hydrolysis to the diketo acids... 

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