Allenyl nitriles

Dihydro-4/7-l,3-oxazines (269) can be prepared in two steps first the addition of allenyl nitriles and 3-aminopropanol to give enamino nitriles (268), and then treatment of these products with a catalytic amount of sodium ethoxide at 200-250°C (Scheme 77) <81H(16)1889>. 

Tnfluoromethyl-substUuted 1,3-dipoles of the propargyl-allenyl type and trifluoromethyl-substituted nitrilium betaines. Tnfluoromethyl- [164, 765] and bis(trifluoromethy])-substituted [166, 167] nitrile ylides have been generated by different methods and trapped with various dipolarophiles to yield [3+2] [768] and [3+1] cycloadducts [769], respectively... 

Allenyl sulfides RSCH=C=CH2 and the same nitrile oxide undergo cycloadditions which occur exclusively or predominantly at the external double bond to give 4-alkylidenedihydroisoxazoles 58 and 5-(methylthio)isoxazoles 59 (226). 

Another method to prepare allenyl ketones uses flash vacuum pyrolysis of the heterocycles 121 (Scheme 7.19) [163], This elimination of carbon monoxide is at least formally a cheletropic reaction. Highly reactive allenes such as esters and nitriles of type 124 or unsubstituted butadienal can be generated if retro-Diels-Alder reaction of 123 or similar precursors, respectively, is performed by flash vacuum pyrolysis [164]. 

As indicated in Section ni.B, deprotonation of a carbamate affords a dipole-stabilized a-amino-organolithium that can be transmetalated with copper salts to form cuprates, thereby expanding the versatility of the organolithium. Suitable electrophiles include enones, alkenyl, alkynyl, allenyl and dienyl carboxylic acid derivatives, nitriles and sulfoxides. Dieter and coworkers have shown that the same process can be accomplished via transmetalation of a stannane (Scheme 36). The procedure is particularly... 

Aniline, N-allenyl-, cycloaddition of nitrile oxide and rearrangement, 60, 304 Anilines, A,7V-dialkyl-3-alkoxy-, lithiation, 56, 260... 

Dipolar compounds (1,3-dipoles), first designated by Huisgen [1], are a class of 4tt-electron species that can be represented by zwitterionic (or ylide) forms with a separation of charge over three atoms. Basically, 1,3-dipoles are categorized into two subclasses, including the allyl type (carbonyl ylides, carbonyl imines, azomethine ylides, azomethine imines, and nitrones) and the propargyl/allenyl type (azides, diazoalkanes, nitrile ylides, nitrile imines, and nitrile oxides), as shown in Scheme 16.1. 

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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