Carbopalladation related compounds

In this latter reaction mode, which is observed much more rarely than /3-dehydropal-ladation, a wide variety of ligands can be coupled to each other with the formation of new C—C, C—H, C— N, C—O, and C—Hal bonds. This section does not cover the numerous cascade couplings in which a number of successive intramolecular additions of 2 onto double bonds is eventually completed by /3-dehydropalladationt as well as the numerous [2 -I- 2 -I- 2] and [4 + 2] cyclotri- and cyclodimerizations of alkynes, enynes, and related compounds. " The Pd(0)-catalyzed Cope rearrangement also will not be considered here, as it proceeds via bis(i7 -allyl)palladium(ll) intermediates. The carbopalladation reactions of aUenes, which have been reviewed recently, are covered in Sect. IV.7. (For new examples see also refs. [10]-[12]). On the other hand, the numerous Pd-catalyzed formal [3 + 2] cycloadditions of trimethylenemethane (TMM) complexes may be classified as carbopalladations of alkenes without subsequent dehydropalladation. As the subject of this section has partially been covered in several newly published reviews, " the attention here will be on the most recent and interesting communications. 

A systematic investigation of cyclic acylpalladation of haloenes, haloynes, and related electrophiles conducted since 1983 [30] has led to the development of three types of cyclic acylpalladation processes (Types I—III Ac-Pd) and Pd-catalyzed carbonylation-induced ketene [2 + 2] cycloaddition (Sect. 3.1). Collectively, these cyclic acylpalladation and related reactions have provided a number of new and attractive routes to cyclic compounds. Significantly, they nicely complement and supplement the non-carbonylative cyclic carbopalladation reactions. Thus, they have become integral and indispensable parts of the carbopalladation-based cyclization methodology. 

Various metal-metal bonded compounds containing relatively electronegative metals, such as Si, Ge, Sn, B, Al, and Zn, can undergo Pd-catalyzed metallometallation, which mostly involves yn-addition to alkynes. One plausible mechanistic scheme involves (i) oxidative addition of metal-metal bonded compounds to Pd, (ii) metallopalladation (pattern 6) leading to yn-addition of metal-Pd bonds, and (iii) reductive elimination (Scheme 12). As such, the overall mechanism resembles that of Pd-catalyzed hydrogenation or hydrosilation, and the critical metallopalladation step must be mechanistically closely related to those of hydropalladation and carbopalladation. These reactions are discussed in detail in Sect. Vn.5. 

Erase, S. and de Meijere, A. (2002) Palladium-catalyzed tandem and cascade carbopalladation -termination with alkenes, arenes and related jr-compounds, mHandbook of Organo-Palladium Chemistry (ed. E.-i. Negishi), John WUey Sons Inc., New York, pp. 1369 05. 

Carbopalladation of Arynes by Arylpalladium Complexes Pd-Catalyzed Annulation Reactions of Arynes. Whereas the Pd-catalyzed annulation of alkynes by aiyl halides has proven to be an effective method for the construction of a wide variety of hetero- and carbocycles similar carbopalladation of arynes were unprecedented until Larock and Zhang reported the synthesis of flu-oren-9-ones 115 through the annulation of arynes by o-haloarenecarboxaldehydes (Scheme 12.57) [100]. Larock s group has also developed a Pd-catalyzed annulation of arynes by 2-halobiaryls, affording polycyclic aromatic and hetCToaromatic compounds such as 116 from simple starting materials. Larock and Cheng have independently reported the related double annulation of arynes by simple aryl halides as an efficient route to functionalized triphenylenes (Scheme 12.57) [101]. 

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