Ethynyl steroids, hydrophosphinylation

There is only a single example of application of this method to the synthesis of biologically interesting compounds. Stockland et al. carried out rhodium-catalyzed hydrophosphinylation of ethynyl steroids of type 185, as shown in Scheme 47.46, to obtain terminal phosphinates or phosphine oxide derivatives 186.As mentioned earlier, the reaction afforded -products exclusively. The authors examined different reaction conditions, with a focus on the green approach hence, solvent-free and aqueous conditions were used in combination with microwave heating. 

Hydrophosphinylation of ethynyl steroids 185 A microwave reactor vial was charged with ethynyl estradiol (100 mg, 0.34 mmol), (Me2PhP)3RhMe3 (6 mg, lOpimol), a magnetic stirring bar, HP(0)Ph2 (68 mg, 0.34 mmol), and water (1.5 mL). The vial was sealed, placed in the reactor, and irradiated. The... 

SCHEME 47.46. Stereospecific, Rh-catalyzed hydrophosphinylation of ethynyl steroids. 

Stockland RA, Lipman AJ, Bawiec IIIJA, Morrison PE, Guzei lA, Findeis PM, Tambfin JF. Remarkable tolerance of ethynyl steroids to air and water in microwave-assisted hydrophosphinylation Reaction scope and limitations. J. Org. Chem. 2006 691 4042-4053. 

Another useful Rh-catalyzed reaction includes Ph2P(0)H addition to the triple bond of ethynyl steroids as air and water insensitive microwave-assisted hydrophosphinylation [91]. The reaction proceeded via the anti-Markovnikov addition, leading to the -/i-isomer. Rhodium complexes with hydrotris(3,5-dimethylpy-razolyl)borate ligand (Tp ) have shown catalytic activity in alkynes hydrophosphinylation with diphenylphosphine oxide [92]. Anti-Markovnikov products ( -)S-isomers) were formed in this reaction in moderate yields of 17-51%. Catalytic performance of Tp Rh(PPh3)2 and Tp Rh(cod) complexes was less efficient than [ClRh(PPh3)4] catalyst in the same conditions. 

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