Carbons, arylations, 2- phenyl triflate

The reactive zwitterions arising from the nucleophilic attack of imines 479 on the benzyne generated in situ from 2-(trimethylsilyl)phenyl triflate 478 proved to be an appropriate molecular scaffold for the capture of CO2 with sufficient electrophilicity to yield 2-aryl-3,l-benzoxazin+-ones 480 (Equation 53). Both substituents of the C=N bond affected the course of the reaction considerably the best yields were achieved by using imines with electron-rich or neutral aryl groups on the carbon, and benzyl or nonbranched chain alkyl substituents on the nitrogen atom. With substituted derivatives of 478, the unsymmetrically substituted arynes led to regioisomeric products <2006JA9308>. 

Tributylstannyl)-3-cyclobutene-1,2-diones and 4-methyl-3-(tributylstan-nyl)-3-cyclobutene-l,2-dione 2-ethylene acetals undergo the palladium/copper-catalyzed cross coupling with acyl halides, and palladium-catalyzed carbon-ylative cross coupling with aryl/heteroaryl iodides [45]. The coupling reaction of alkenyl (phenyl )iodonium triflates is also performed by a palladium/copper catalyst [46],... 

Aryl chlorides were found to successfully couple with methyl phenyl sulfoxi-mines in a series of experiments reported by Harmata s group [129]. Using palladium acetate and binap with a large excess of aryl chlorides as coupling partners and cesium carbonate as the base, yields between 10-94% were obtained after one or two 1.5-h irradiation periods at 135 °C. Switching to an aryl triflate and use of an excess of the sulfoximines (5 equiv.) furnished an impressive 94% yield (Scheme 15.63). 

The Pd(0) catalyst precursor can be added to the reaction vessel in its zerovalent or 2+ oxidation states. Examples of typical catalyst precursors are Pd(PPh3>4, Pd(dba)2, and PdCl2(dppf). Heterogeneous Pd-catalysts are also effective. For example palladium supported on carbon (Pd/C) is an effective catalyst for the coupling of aryl halides and triflates with phenyl boronic acid 146J47),... 

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