Tetrahydrophosphepine

Reaction of the regioisomers of tetrahydrophosphinine oxide (51) with Na0H-H20-CHCl3 under phase-transfer conditions was found to afford tetrahydrophosphepine oxides (52) through an unexpected path involving isomerization of (51) and cyclopropanation via Michael addition of CCls. (Scheme 21). 

The use of (Z)-l-ferf-butyl-2,3,6,7-tetrahydrophosphepine ligand was thus identified as a superior catalytic system for the arylation of heterocycles with bromoarenes, with higher conversions and low incidence of hydrodehalogenation (Scheme 17). Under typical reaction conditions, the heterocycle (1 equiv.), ArBr... 

The scope of the reaction is broadened by the use of the tetrahydrophosphepine ligand. In addition to heterocycles that were reactive with PCy3 or cyclohexyl-phobane as ligands, 4,5-dimethylthiazole can be arylated. The scope with respect to the bromoarene partner is also broadened to include electron-rich bromoarenes and heteroaryl bromides such as 3-bromothiophene, 5-bromo-iV-methylindole, 5-bromobenzofuran, and 5-bromobenzothiophene. Functional groups including sulfoxides, chlorides, fluorides, ketones, esters, primary and secondary amides, phenols, anilines, and pyridines can be tolerated under these conditions. Sterically hindered and/or ortho substituted substrates are unreactive, but meta and para substituted substrates are well-tolerated. 

Scheme 18 Proposed catalytic cycle for the C-H arylation of arenes through iV-heterocyclic carbene formation with tetrahydrophosphepine ligands [104]...

A 3-phospholene oxide, a 1,2,3,6-tetrahydrophosphinine oxide and a 2,3,4,7-tetrahydrophosphepine oxide were prepared by a novel molybdenum-catalyzed asymmetric ring closing metathesis (Scheme 2). ... 

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