Carbenoid isonitrile

In this chapter, we provide the necessary background concerning the formation of zir-conacycles, then briefly review the insertion of carbon monoxide and isoelectronic isonitriles into organozirconocenes. We then describe in more detail the insertion of a-halo-a-lithium species (R1R2CLiX, carbenoids [7]), which may be viewed as taking place according to a conceptually similar mechanism. 

Insertion of isonitriles and carbenoids into the B-B and B-Si bonds have recently been developed as a method for synthesizing geminal bis(boryl) and boryl-silyl compounds (Scheme 24). The insertion of alkyl and aryl isonitriles into the B-Si bond proceeded at room temperature to provide monomeric (boryl)(silyl)imines 227.388,389 Alkylidene... 

Scheme 24 Insertion of carbenoids and isonitriles into B-B and B-Si bonds.

Very common Cl fragments bound to a polymeric support are carbenoids. The simplest carbenoid is CO itself, which can be used in transition metal-catalyzed insertions between benzofuran-3yl palladium and a nucleophile such as trifluoroethanol [161]. One of the most common carbenoids is isonitrile, which is used in a large number of multicomponent reactions. Diazoalkanes have often been used as carbene precursors, since they can be readily obtained from support-bound anions and sulfonyl azides [252]. Commonly, diazoalkanes are converted transi-... 

Isonitriles often show carbenoid reactivity, so it is not surprising that benzyl isocyanide (31) adds readily to 1,2,4,5-tetrazines (Scheme 4). Again the (4-1-1) cycloaddition step to (32) is followed by... 

Compared with five-membered metallacycles, relatively fewer reports are known on the preparative methods and reaction chemistry of six-membered metallacycles. Whitby and coworkers have systematically investigated insertion of carbenoids into five-membered zirconacycles and developed a number of interesting six-membered zirconacycles [17, 26]. Isonitriles, 1-halo-l-lithioalkenes, allenyl carbenoids, allyl carbenoids, propargy carbenoids, benzyl carbenoids, and 1-nitrile-1-lithio epoxides can all insert into zirconacyclopentanes and zirconacyclopentenes to afford various six-membered zirconacycles (Eqs. 23,24). 

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