Syntheses of symmetric and unsymmetric 2,6-bis(phosphino)phenols
Compounds bearing the structural motif of 2,6-bis(phosphino)phenol have been synthesized via two general methods. Double lithium-halogen exchange occurred in low-temperature reactions of O-protected (by methyl- or tetrahydropyranyl groups) 2,6-dibromo-4-methylphenol derivatives with BuLi (2 equivalents); quenching the reaction mixtures with chlorophosphines ClPR 2 (R = Ph, iPr) and corresponding O-deprotection yielded symmetrically substituted 2,6-bis(phosphino)phenols. Sequential incorporation of -PR2 functionalities was accomplished via single lithium-halogen exchange (1 eq. of BuLi) of tetrahydropyranyl-protected 2,6-dibromo-4- methylphenol followed by ClPR2 quenches, thus enabling the syntheses of unsymmetric 2,6-bis(phosphino)phenols. Such compounds were also obtained via sequential ortholithiations of tetrahydropyranyl-protected 4-tert-but ylphenol, followed by ClPR2 quenches. All of the new compounds have been characterized by spectrometric methods (1H and 31P NMR, and mass spectrometry). In addition, two of the compounds, 1-(diphenylphosphino) -3-(diphenylphosphoryl)-2-methoxy-5-methylbenzene (3a-ox) and 1,3-bis(diphenylphosphino)-2-methoxy-5-methylbenzene (6a) have also been characterized via single crystal X-ray diffraction experiments. © 2006 Wiley Periodicals, Inc.
Syntheses of symmetric and unsymmetric 2,6-bis(phosphino)phenols.
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