Cyclic phosphinic acid functionalization

Blaser and Spencer used aroyl halides in place of aryl halides, with aroyl chlorides being of specific interest as ubiquitous, relatively cheap compounds ( Blaser reaction ) [24], This latter reaction is normally conducted in aromatic solvents phosphines are not used here as catalyst ligands since they fully inhibit the reaction. In the same way, benzoic acid anhydrides can be used as the aryl source in combination with PdCl2 and catalytic amounts of NaBr [79]. In this reaction, one of the arenes is used in the coupling reaction by elimination of CO, whereas the other benzoate serves as the base. The benzoic acid thus formed can easily be recycled into the anhydride. The use of aryl and vinyl triflates according to Cacchi [25] and Stille [26] extends the scope of the Heck coupling to carbonyl compounds phenol derivatives act via triflate functionalization as synthetic equivalents of the aryl halides. The arylation of cyclic alkenes [27], electron-rich vinyl ethers [28], and allylic alcohols [29] is accessible through Heck reactions. Allylic alcohols yield C-C-saturated carbonyl compounds (aldehydes) for mechanistic reasons (y9-H elimination), as exemplified in eq. (6). 

If water-soluble phosphine ligands are applied, extremely mild reaction conditions can be achieved. Especially, Pd(TPPMS)3, which converts 4-iodotoluene, is tolerant of a broad range of functional groups, including those present in unprotected nucleotides and amino acids [6]. Interestingly, even the coupling of a donor-substituted iodoarenes and cyclic olefins can be conducted by palladium acetate with TPPTS at only 25 °C in aqueous acetonitrile. However, the low rates observed require a reaction time of up to 48 h for high conversions [12]. 

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