Carbonyl phosphonylation via[1 N ,3 E ]-bifunctional reagents. Probing mechanistic and reactivity features through chemical and isotopic labelling

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Abstract
A range of organophosphorus(III) esters of the general form {DIAM}PX(SiR3)n{X = O, n= 1; X = N, n= 2; R3= Me3, Ph3, tBuMe2, Et3; DIAM =N,N′-(CH2NMe)2 and N,N′-CH2(CH2NMe)2} has been prepared via reaction of {DIAM}PCI with R3SiOH or LiN(SiMe3)2 respectively. These esters will phosphonylate aldehydes via the Abramov reaction to afford α-siloxyphosphonate esters cleanly and in high yields. The mechanism of the Abramov reaction using {DIAM}POSiR3 reagents has been investigated by (i)18O isotopic labelling experiments which reveal that reaction proceeds with exclusive [O–Si] rather than [P–O] bond cleavage which, in turn, supports a mechanism with overall retention of configuration at phosphorus, (ii) double crossover experiments which support intramolecular silylgroup transfer and (iii) manipulations of the electron-donating properties of the carbonyl substrate which suggest that [P–C] bond formation is rate determining. Further tuning of the phosphonylation reaction is possible by manipulating (a) the nature of the phosphorus-coordinated donor atoms in the chelate ring, (b) the size and rigidity of the chelate ring, (c) the ester residue donor atom X and (d) the silicon substituents R.

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