Journal of the Chemical Society. Perkin transactions I p. 769 - 775 (1996)
Update date:2022-08-11
Topics:
Dang, Hai-Shan
Roberts, Brian P.
α-Diazo ketones RC(O)CH=N2 react with tributyltin hydride at 60°C in benzene to give the corresponding α-stannyl ketones RC(O)CH2SnBu3, which exist in equilibrium with the stannyl enol ether tautomers R(Bu3SnO)C=CH2. The reactions are initiated by di-tert-butyl hyponitrite and follow a free-radical chain mechanism. Triphenyltin hydride and tris(trimethylsilyl)silane [(TMS)3SiH] react similarly, the latter to yield the α-silyl ketone RC(O)CH2Si(TMS)3 which does not isomerise to the more stable silyl enol ether R[(TMS)3SiO]C=CH2 under the reaction conditions. This result indicates that TMS3Si. reacts at the α-carbon atom of the α-diazo ketone to give R(CO)CHSiTMS3, probably via an initial diazenyl radical adduct; triorganotin radicals are assumed to react in the same way. When the group R in the α-diazo ketone is but-3-enyl, the intermediate α-metalloalkyl radical undergoes 5-exo-cyclisation. Allyltributylstannane reacts with α-diazo ketones and with ethyl α-diazoacetate in refluxing benzene, in the presence of 2,2′-azo(2-methylpropionitrile) as initiator, to give butenyl ketones RC(O)CH2CH2CH=CH2 and ethyl pent-4-enoate, respectively, after a hydrolytic work-up.
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