Cyclization allylic alkynoates

The key point in divalent Pd-catalyzed cyclization of allylic alkynoates is the method of quenching of the carbon-paUadium bond formed after cyclization. In order to develop a divalent Pd-catalyzed reaction, a divalent palladium species must be regenerated in the quenching of the carbon-paUadium bond. Lu and co-workers developed different quenching methods for the carbon-palladium bonds, for example, /3-heteroatom elimination, copper halide mediated oxidative cleavage, and carbonylation and protonolysis of... 

It has been postulated that these cycloheptenes must be formed via a 7r-allylruthenium intermediate (Scheme 59). The cyclization is initiated by activation of the allylic C-H bond to form the 7r-allylruthenium 234. The 1-exo-dig carboruthenation of the alkynoate 234 produces the hydrido-ruthenium enolate 235. Equilibration of 235 followed by reductive elimination gives the corresponding cycloheptenes 237 and regenerates the cationic ruthenium complex. 

The cyclofunctionalization of 4-alkynoic and 5-alkynoic acids generates y-alkylidene-y-lactones and 5-alkylidene-S-lactones, respectively (equation 76 and Table 22). The initial products from the reactions catalyzed by mercury or silver salts undergo protiodemetallation under the reaction conditions. The vi-nylpalladium intermediates undergo either protiodemetallation or coupling with an added allyl halide. The palladium(II)-catalyzed cyclization of 3-alkynoic acids proceeds by 5-endo closure to give 3-buten-4-olides (Table 22, entry 2).50 190... 

Addition of BuaSnH to enynes is regio- and stereoselective, thus making 2-stan-nyl-1,3-dienes readily available. Cyclization of allyl 2-alkynoates with simultaneous carbonylation is a useful way to access functionalized y-lactones. Nonconjugated dienes undergo reactions at both ends with aryl iodides and amines the products are allylamines bearing an w-aryl group. ... 

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