FACTORS IN THE CONTROL OF PRODUCT COMPOSITION IN THE REACTIONS OF TRIALKYL PHOSPHITES WITH α-HALOGENOACETOPHENONES IN ALCOHOLIC MEDIA

References

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• Results are quoted for 15–20:1 mole ratios of phosphite to α-halogenoacetophenone (see Experimental) and demonstrate trends in product composition for various changes in reaction parameters. (RO)2PHO and (RO)2P(O)Me are also formed as by-products. It should be noted that the absolute values of the yields obtained are influenced by the reactant ratios, higher percentages of α-hydroxyphosphonate being formed with more nearly equivalent quantities of reactants (see e.g. preparations by methods 1 or 2 in the experimental section)
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• Ketophosphonates have previously been reported as minor products in the reactions of certain α-bromo-ketones with phosphite esters in alcoholic media (cf. refs. 4, 6, 8). Such products were not detectable under the conditions of our experiments, which were carried out at lower temperatures. It is likely that protonation of carbonyl oxygen (or at least coordination to the alcoholic proton) will be favoured under these conditions and that phosphite addition to the carbonyl group, leading to hydroxyphosphonate or vinyl phosphate formation, will be preferred
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• Magnetic non-equivalence of the two alkoxy groups was observed for both methyl and ethyl esters. The effect is attributed to restricted rotation about the P-C bond resulting from intramolecular hydrogen-bonding and will be discussed elsewhere. Previous examples of non-equivalence in dialkyl phosphonates have been confined to the α-methylene protons in the same alkyl group in the vicinity of a chiral or prochiral phosphorus atom (C. D. Hall, R. Ardrey, R. Dyer, and P. G. Le Gras, J. C. S. Perkin II, 1977, 1232)
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