Regioselective internal phosphine group

The palladium-catalyzed reaction of iodobenzene and an allenyl malonate provided vinylcyclopropane in a highly regioselective manner (Scheme 16.7) [11, 12]. A jT-allylpalladium complex, generated by the addition of PhPdl to a 2-allenyl malonate, can be trapped by an internal malonate anion to afford a vinylcyclopropyl derivative. The site selectivity in this cyclization is dependent on the nature of the entering RX groups, catalytic systems involving phosphine ligands, solvents and bases. 

Cycloaddition of alkynes is an easy and efficient approach towards the synthesis of benzene derivatives [21]. However, fluorine-containing alkynes are rarely shown to undergo such reaction [22]. [RUj(CO)32], with phosphine or some phosphine derivative as additive, is able to cyclotrimer-ize the trifluoromethyl group substituted internal alkynes [23]. Particularly, when 2-(diphenylphosphino)benzonitrile (2-DPPBN) is used, the cyclotrimerized unsymmetrical benzene derivative forms in 77-92% yield with more than 98% regioselectivity depending upon the substituent in Ar... 

Well-defined palladium complexes are interesting from an academic point of view. In 2013, Shi, Cao and their co-workers prepared a well-defined fer-rocenyl functionalized NHC-palladium complex and applied it as an efficient catalyst for Larock heteroannulation. 2,3-Disubstituted indoles were isolated in good yields (69-90%) with high regioselectivity from the reactions between 2-iodoanilines or 2-bromoanilines and their derivatives with various internal alkynes (Scheme 2.98). The reactions occur in a broad scope and with a high tolerance of functional groups. NHC-palladium complexes could be excellent candidates to replace expensive palladium-phosphine complexes for Larock indole catalysis. 

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