DIASTEREOSELECTIVITY IN THE MUKAIYAMA-MICHAEL REACTION EMPLOYING ALPHA-ACYL BETA,GAMMA-UNSATURATED PHOSPHONATES

The unique electronic and structural nature of the alpha-acylphosphona te functional group affords both dimeric and chelated complexes of die thyl crotonyl phosphonate (1; DECP) with stannic chloride (SnCl4). The dimeric complex, SnCl4 .(DECP)(2) (5) results from the coordination o f two DECP molecules, ligated via the phosphoryl oxygens to the tin at om. The chelated complex, SnCl4 .(DECP) (6), is best represented with both phosphoryl and carbonyl oxygens coordinated to the metal center. Both metal Ligated and chelated complexes have unique (CP)-C-13-P-31, and Sn-119 NMR spectra. In complex 5, the C-13 NMR resonances attribut ed to the carbonyl carbons were shifted upfield of free DECP. A monoco ordinating Lewis acid, BF3 . OEt(2), produced a similar chemical shift trend in both the C-13 and P-31 NMR spectra of the BF3 . DECP complex . Essentially quantitative yields and moderate diastereomeric excesses favoring anti (or trans) diethyl yl-6-(trimethylsilyloxy)-2-dihydropy ranphosphonate (3) and diethyl 5-phenyl-3,4-dimethyl-1,5-dioxopentanep hosphonate (4) were obtained from both chelated and dimeric SnCl4 .(DE CP)(n) (n = 1, 2) when treated with either diastereomeric (Z)- or (E)- 1-phenyl-1-(trimethylsilyloxy)-1-propene 2. Diethyl crotonylphosphonat e (1), 3, and 4 were fully characterized.