Acae-promoted rearrangement of an alkylaluminophosphonate tetramer to a decamer

Reaction of MeP(O)(OH)(2) with (Bu3Al)-Bu-t at low temperature and subseque nt trimethylsilylation of the crude reaction product with Me3SiNMe2 yielded the cyclic dimer [(Bu2AlO2P)-Bu-t-(OSiMe3)Me](2) (1). In contrast, reactio n of MeP(O)(OH)(2) with (Bu3Al)-Bu-t in refluxing toluene/THF yielded a mix ture of [(BuAlO3PMe)-Bu-t](4) (2), [(BuAlO3PMe)-Bu-t](6) (3), and [(BuAlO3P Me)-Bu-t](10) (4). Crystallization and sublimation of the crude mixture gav e compound 2 in 54% yield. Small quantities of pure 3 were obtained by frac tional crystallization of the remaining reaction products. Crystalline 3 wa s also obtained by slow diffusion of a CHCl3 solution of acetylacetone into a solution of 2 in poly(ethylene oxide)/CHCl3 gel. It was not possible to obtain reproducible yields of pure 4 by fractional crystallization of the c rude mixture of 2-4. Instead, compound 4 was obtained in 86% yield by an ac etylacetone-promoted rearrangement of 2. In the absence of acetylacetone, C DCl3 solutions of 4 rearrange to a mixture of 2, 3, and 4 over a period of days. The role of acetylacetone in the rearrangement of 2 to 4 has not been elucidated. Compounds 1-4 were characterized by multinuclear (H-1, C-13, P -31) NMR spectroscopy, infrared spectroscopy, mass spectrometry, and elemen tal analysis. The molecular structures for compounds 2-4 were determined by X-ray crystallography.