Synthesis applications with zinc reagents

Tandem 1,4-addition to cycloalkenones constitutes an extremely versatile and elegant methodology for the synthesis of 2,3-disubstituted cycloalkanones, as is evident from its application in areas such as prostaglandin synthesis. Noyori et al. have reported the use of organozinc reagents in copper-catalyzed tandem additions [64]. The zinc enolate resulting from the catalytic enantioselective 1,4-addition of Et2Zn to cyclohexenone reacts readily with an aldehyde in a subsequent aldol condensation. 

Several reports have appeared of the application of unusual organometallic reagents in phosphine synthesis. Treatment of 2-lithiopyridine with anhydrous zinc chloride results in the formation of a 2-pyridylzinc reagent which can be used to introduce the 2-pyridyl group at phosphorus in a controlled manner. Thus, e.g., in its reaction with phenyldichlorophosphine, the 2-pyridyl-(phenyl)chlorophosphine (15) is formed. This has then been converted via the phosphide route into a new class of binucleating ligands (16). The sterically crowded dichlorophosphine (17) (accessible from the reaction of phosphorus trichloride with lithium diphenyl(2-pyridyl)methanide) is converted into the thermally stable phosphirane (18) on treatment with calcium, strontium or barium cyclooctatetraenide.The reaction of phenyldichlorophosphine with the readily accessible titanacycle (19) affords a convenient route to the phosphetene (20). ... 

---