Synthesis of Bulky Arylphosphanes by Rhodium‐Catalyzed Formal [2+2+2] Cycloaddition Reaction and Their Use as Ligands

Abstract

Treatment of 1-alkynylphosphane sulfides with 1,6- or 1,7-diynes in the presence of a cationic rhodium catalyst results in a formal [2+2+2] cycloaddition reaction to afford the corresponding aromatic phosphane sulfides. The aromatic rings formed in the cycloaddition naturally bear one or two substituents at the ortho positions to the phosphorus atom, which creates a sterically hindered environment around the phosphorus atom. The following desulfidation of the products is facile under radical conditions or with the aid of tris(dimethylamino)phosphane, providing the corresponding bulky phosphanes. Dicyclohexyl(2,6-diphenylaryl)phosphane, which is available through this sequence, proves to serve as an efficient ligand in palladium-catalyzed cross-coupling amination reactions.

Preparation and synthetic applications of alkene complexes of group 9 transition metals in [2+2+2] cycloaddition reactions

“…The synthesis of highly substituted, bulky arylphosphines and triarylarsines was accomplished by Yorimitsu and Oshima et al by using internal diynes and diphenylalkynyl thiophosphine or diphenyl(phenylethynyl)-arsine. 60 Their catalyst system comprised of [Rh(COD)Cl] 2 (16) with BINAP and AgBF 4 . In refluxing 1,2-dichloroethane, the AgBF 4 promotes anion exchange from 16 to provide the active cationic Rh(I)-complex.…”

Phosphines and related C–P bonded compounds

“…115 Both tris(trimethylsilyl)silane, (in the presence of a radical initiator in benzene), and tris(dimethylamino)phosphine have been used for the reduction to the phosphines (85) of the related sulfides obtained by a rhodium-catalysed formal [2 þ 2 þ 2] cycloaddition reaction between heteroatom-bridged dialkynes and alkynylphosphine sulfides. 116 The reduction of tertiary phosphine oxides with diisobutylaluminium hydride (DIBAL-H) has been the subject of a detailed study, resulting in a significant improvement in experimental protocols and making DIBAL-H a much more attractive reagent. 117 In a new development, it has been shown that alkylene bis(diphenylphosphine oxides) can be selectively reduced to the related bis(phosphine) monoxide under exceptionally mild conditions using a combination of triflic anhydride and a thiol.…”