Perkow reaction mechanism

Sekine, M., Okimoto, K., Yamada, K., and Hata, T., Silyl phosphites. 15. Reactions of silyl phosphites with a-halocarbonyl compounds. Elucidation of the mechanism of the Perkow reaction and related reactions with confirmed experiments, /. Org. Chem., 46, 2097, 1981. 

In spite of many previous studies on the mechanisms by which trialkyl phosphites interact with a -halogenocarbonyl compounds, the reactive intermediates which lead to ketophosphonate (Arbuzov reaction) and to vinyl phosphate (Perkow reaction) have in no cases been clearly identified. It is generally believed (JL), however, that the Arbuzov product 4 results from initial attack by phosphorus at the cf-carbon atom, whereas the Perkow product 7 is formed by initial attack at the carbonyl carbon atom, followed by migration of phosphorus from carbon to oxygen (Scheme 1). 

The mechanism of the Perkow reaction has been a subject of some debate but is now generally thought to proceed by initial attack of phosphorus at the carbonyl carbon atom, not by rearrangement of a Michaelis-Arbuzov intermediate 5.77,78... 

Miller, J.A., Reactions of dimethyl phosphite with tetracyclone, Tetrahedmn Lett., 11, 3427, 1970. Borowitz, I.J., Firstenberg, S., Borowitz, G.B., and Schuessler, D., Organophosphorus chemistry. Part 17. Kinetics and mechanism of the Perkow reaction, 7. Am. Chem. Soc., 94, 1623, 1972. 

Many different mechanisms have been proposed for the Perkow reaction.2-4 It involves nucleophilic attack of the phosphite at the carbonyl carbon and affords a zwitterionic intermediate 5 which rearranges to form a cationic species 6 that subsequently dealkylates to give the corresponding vinyl phosphate 7. The conversion proceeds via a Michaelis-Arbuzov cleavage of an alkoxy group by halide ion as shown. 

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