Intramolecular, Pd/Cu-Co-catalyzed P–C Bond Cleavage and Addition onto an Alkyne: A Route to Benzophospholes

Abstract

Under Pd(II)/CuI cocatalysis, o-diarylphosphinophenylalkynes cyclize in boiling toluene via C-P bond cleavage and arylphosphination of the C≡C bond. This protocol provides an unprecedented atom- and step-efficient access to optoelectronically and biologically interesting benzophospholes.

A Calixarene‐Decorated Phosphole Oxide

“…The formation of arylation product 10 is compatible with the mechanism proposed by Mathey that involves transient phenylpalladium intermediates. [11] Solutions of 10 were not luminescent when irradiated at 365 nm.…”

“…The synthesis began with the preparation of calixarenyl-(2-diphenylphosphinophenyl)ethyne (5, Scheme 1), which we considered as a potential candidate for a P-alkyne coupling reaction similar to that recently described by Mathey et al for phosphole synthesis. [11] Mono-bromo calixarene 1 was converted into 2 in 52 % yield through Sonogashira coupling. Subsequent deprotection with K 2 CO 3 in CH 2 Cl 2 /MeOH afforded 3.…”

“…the precursor of 9, which was not isolated because of its high sensitivity towards oxygen) is probably similar to that recently proposed by Mathey et al, although the exact role of CuI is unclear, despite its necessity. [11] The main features of this reaction are cleavage of a P-Ph bond followed by P-addition to the C≡C bond. As expected for a benzophosphole oxide, the product absorbs strongly in the UV region [ε = 7 240 M -1 cm -1…”

Synthetic Applications of Transition‐Metal‐Catalyzed C−P Bond Cleavage

“…A palladium/copper cocatalyzed intramolecular phosphination of the C≡C bond of o ‐diarylphosphinophenylalkynes 82 was developed by Mathey and co‐workers (Scheme ) . The lone pair on phosphorus is crucial for this reaction; no reaction was observed with phosphine oxide or BH 3 complex.…”

“…Ap alladium/copperc ocatalyzed intramolecular phosphination of the CCb ond of o-diarylphosphinophenylalkynes 82 was developed by Matheya nd co-workers (Scheme 27). [45] The lone pairo np hosphorus is crucial for this reaction;n or eaction was observedw ith phosphine oxide or BH 3 complex.I tw as proposed thatt he alkynyl group helpedt ob ring the reactive palladium species into the proximity of CÀPb ond activation and facilitated the subsequent phosphination process to give benzophosphole 85.T he role of CuI is as-yet unclear.L ater, Matt and co-workerss howed that the palladium/copper cocatalysts could be used to synthesize the interesting calixarenedecorated benzophosphole. [46] The chelation-assisted catalytic activation of the CÀP(O) bond was demonstrated by Wu and co-workerst hrough insertion of palladium into as eries of pyrazole-derived substrates 86 under mild conditions (Scheme 28).…”