Alkynyl carbonates, addition reactions

Although many examples of addition reactions of carbon nucleophiles to the C=C bond of a (l-alkynyl)carbene complex have been reported (vide infra), to date there are few reports of reactions by which a carbon-carbon bond is formed to Cl, thus leaving the C=C bond unchanged. Reactions of the latter type involve insertion of an alkyne into the M=C bond of a (l-alkynyl)carbene complex 1 (Scheme 1). 

Now that the properties of carbon-carbon double bonds have been examined in detail, it s time to have a brief look at their relatives, carbon-carbon triple bonds. Not surprisingly, what you will find will be very similar to what you ve just. seen. Addition reactions will mtike up the main portion of triple bond chemistry. An iinporlani feature is the hydrogen attached to triply bonded carbon It is unusually acidic, allowing ready removal by strong bases to form a new and synthetically useful class of carbanions called alkynyl anions. 

Reactions of Alkynyl Amines In 2004, Shimada et al. reported that platinum-catalyzed intramolecular carbon-nitrogen bond addition reaction, called... 

Terminal alkynes react with propargylic carbonates at room temperature to afford the alka-l, 2-dien-4-yne 14 (allenylalkyne) in good yield with catalysis by Pd(0) and Cul[5], The reaction can be explained by the transmetallation of the (7-allenylpailadium methoxide 4 with copper acetylides to form the allenyKalk-ynyl)palladium 13, which undergoes reductive elimination to form the allenyl alkyne 14. In addition to propargylic carbonates, propargylic chlorides and acetates (in the presence of ZnCb) also react with terminal alkynes to afford allenylalkynes[6], Allenylalkynes are prepared by the reaction of the alkynyl-oxiranes 15 with zinc acetylides[7]. 

In addition to alcohols, some other nucleophiles such as amines and carbon nucleophiles can be used to trap the acylpalladium intermediates. The o-viny-lidene-/j-lactam 30 is prepared by the carbonylation of the 4-benzylamino-2-alkynyl methyl carbonate derivative 29[16]. The reaction proceeds using TMPP, a cyclic phosphite, as a ligand. When the amino group is protected as the p-toluenesulfonamide, the reaction proceeds in the presence of potassium carbonate, and the f>-alkynyl-/J-lactam 31 is obtained by the isomerization of the allenyl (vinylidene) group to the less strained alkyne. 

Tungsten alkynyl Fischer carbene complexes are excellent dienophile partners in the classical Diels-Alder reaction with 1-azadienes (see Sect. 2.9.2.1). On the contrary, the chromium-derived complexes exhibit a different behaviour and they react through a [4S+3C] heterocyclisation reaction to furnish azepine derivatives [116] (Scheme 68). The reaction is initiated by a 1,2-addition of the nitrogen lone pair to the carbene carbon followed by a [l,2]-Cr(CO)5 shift-pro-... 

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