Palladium-Catalyzed Suzuki–Miyaura Cross-Couplings with 2-Diethylphosphonato-Substituted Aryl- and Naphthylboronate Esters as the Nucleophilic Partner: A Complementary Approach to the Synthesis of Biaryl Monophosphonates

Abstract

This paper reports the first examples of Suzuki–Miyaura cross-couplings involving aryl- and naphthylphosphonate-based boronate esters as the nucleophilic partner. A systematic comparison of the performance of biaryl-like KITPHOS- and XPHOS-based systems revealed that, between them, an electronically and sterically diverse range of substrates can be coupled with remarkable efficiency to afford high yields of the corresponding biaryl and heterobiaryl monophosphonates. The use of an aryl- and naphthylphosphonate-based boronate ester as the coupling partner presents an alternative and potentially complementary pathway to existing couplings in which the aryl- or naphthylphosphonate unit is typically introduced as the electrophile. The potential advantages associated with the use of this new class of coupling partner were clearly demonstrated by the palladium-catalyzed reaction between diethyl [2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]phosphonate and 1-bromo-2-methoxynaphthalene that gave the corresponding biaryl monophosphonate in 56% yield, a marked improvement on the 6% yield obtained from the reaction between 2-methoxy-1-naphthylboronic acid and diethyl (2-bromophenyl)phosphonate with the same catalyst under the same conditions. The potential utility of this new coupling combination was demonstrated by reducing one of the products, 2-methoxy-1-(2′-diethoxyphosphorylphenyl)naphthylene, to the corresponding primary phosphine, which was subsequently converted into a diastereoisomeric mixture of the R,R-hexane-2,5-diol-derived phospholane in reasonable yield.