Ruthenium-Catalyzed C–H Activation/Cyclization for the Synthesis of Phosphaisocoumarins

Abstract

An efficient and cost-effective ruthenium-catalyzed oxidative cyclization of phosphonic acid monoesters or phosphinic acids with alkynes has been developed for the synthesis of a wide range of phosphaisocoumarins in good to excellent yields under aerobic conditions. A multitude of arylphosphonic acid monoesters and arylphosphinic acids having electron-donating and -withdrawing groups were oxidatively cyclized. Various diarylacetylenes, dialkylacetylenes, and alkylarylacetylenes effectively underwent the ruthenium-catalyzed oxidative cyclization. A substrate possessing benzoic acid as well as a phenylphosphonic monoester moiety was smoothly cyclized with hex-3-yne to afford a compound having both isocoumarin and phosphaisocoumarin moieties. Alkenylphosphonic monoester afforded phosphorus 2-pyrone through oxidative cyclization with alkyne. Competition experiments between diaryl- and dialkylalkynes and between diarylacetylenes having p-methoxy and p-chloro groups gave results which showed that the present oxidative cyclizations were not affected by the electronic effects of alkynes. Mechanistic studies revealed C-H bond metalation to be the rate-limiting step.

Weakly Coordinating Directing Groups for Ruthenium(II)‐ Catalyzed CH Activation

“…Phosphaisocoumarins 19 were synthesized by the ruthenium(II)‐catalyzed oxidative coupling of phosphonic acid monoesters or phosphinic acids 18 with alkynes 14 (Scheme ) 23. A broad range of arylphosphonic acid monoesters and arylphosphinic acids 18 containing electron‐donating or electron‐withdrawing groups was found to be reactive with various diarylacetylenes, dialkylacetylenes, and alkylarylacetylenes 14 at a relatively high catalyst loading of 20 mol%.…”

Phosphorus‐Directed C−H Borylation

“…Examples of methods that could afford late‐stage functionalization of organophosphorus moieties through C−H functionalization began to be introduced in 2011 [80–88] . These transformations have been detailed in two recent reviews [89–90] and highlight the pioneering work by Kuninobu and Takai, [91] Satoh and Miura, [92–95] Glorius, [96] Kim and Lee, [97–105] Moon, [106] Yang, [107–109] and Park and Chang [110–111] . Among these valuable transformations are examples of C−H alkylation, alkenylation, arylation, amination, oxygenation, and cyanation.…”

Copper‐vitamin B6 coated on maghemite nanoparticles: A new convenient dual catalysis system to synthesize α‐aminonitriles from benzyl alcohols

“…In addition, they are stable in the presence of air and water and usually be obtained from biologic and natural compounds especially those are inexpensive and could be easily handled [14] Hence, the combination of organocatalysts with transition metals [15] which are chemo, enanthio-and diastereo-selective, also, recoverable (because of its heterogenous character) with high yields, can lead to the creation of a versatile catalysis system. Aminoacids [16] Bronsted acid [17] chelating and hydrogen bond catalysts [18] with transition metals are examples of organocatalysts.…”