Carboannulation reactions

A new and related carboannulation reaction is possible, that involves insertion of alkynes to aryl or alkenyl palladium intermediates, and subsequent cyclization onto an aromatic ring already present in the substrate [252], The cyclization of the enol triflate 509 to give 510 is an example. The reaction was applied to the synthesis of the indolocarbazole derivative 512 from the iodobisindole 511 [253],... 

An efficient carboannulation proceeds by the reaction of vinylcyclopropane (135) or vinylcyclobutane with aryl halides. The multi-step reaction is explained by insertion of alkene, ring opening, diene formation, formation of the TT-allylpalladium 136 by the readdition of H—Pd—I, and its intramolecular reaction with the nucleophile to give the cyclized product 137[I08]. 

A series Pd-catalyzed annulation reactions have been developed by the reaction of o-heterosubstituted iodoarenes 68 and 69 with 1,2-, 1,3- and 1,4-dienes. In the reaction of o-iodoaniline with 1,3-cyclohexadiene (70), the 7i-allyl intermediate 71 reacts with the aniline moiety to give 72 [32, 33]. Carboannulation of the malonate derivative 73 with the 1,3-diene 74 gives 75 in high yield [33a]. 

Dienes (allenes) are also used for heteroannulation with 68 and 69. The eight-membered nitrogen heterocycle 78 is constructed by the reaction of 1,2-undecadiene (77) with o-(3-aminopropyl)iodobenzene (76) [34]. The lactones are prepared by trapping the 7i-allyl intermediates with carboxylic acids as an oxygen nucleophile. The unsaturted lactone 81 is prepared by the reaction of /1-bromo-v,/ -unsaturated carboxylic acid 79 with the allene 80 [35]. In the carboannulation of 82 with 1,4-cyclohexadiene (83), the 1,3-diene 85 is generated by / -elimination of 84, and the addition of H-PdX forms the 7i-allylpalladium 86, which attacks the malonate to give 87 [36],... 

The Larock method for annulation between vicinal iodo-arylamines and 1,2-dienes in the preparation of indoles can be adapted for preparation of azaindoles using corresponding azine substrates. Thus, substituted-3//-pyrrolo[2,3-fc]pyridin-3-ones can be prepared from 2-amino-3-iodopyridine derivatives by a palladium carboannulation process with al-lenic compounds (Scheme 104). The bicychc products, the methylene derivatives 308, and the alkylidenes 309 can be oxidatively cleaved with ketone formation. The reaction may proceed by formation of a pyridinylpaUadium complex followed by the rr-allyl complexa-tion of aUenic derivatives 310. Since the polar substituents on terminal carbons of the 7r-allyl system influence the regiochemistry of the reactions, nucleophilic attack of the nitrogen atom on the most electron-deficient carbon atom of the rr-allyl system affords either of the... 

Intramolecular addition of a 1,3-diene having a carbon nucleophile in the side chain is catalyzed by Pd(II), leading to an overall 1,4-oxidation of the diene (Scheme 10). Allylsilane can be used as a carbon nucleophile in the Pd(II)-catalyzed carboannulation. The reaction of the 1,3-diene (E)-29 with a catalytic amount of Li2PdCl4 in the presence of p-benzoquinone (1.5 equiv), which acts as an oxidant of Pd(0) generated in the reaction, and LiCl (2 equiv) in acetone-acetic add (2 1) gives a mixture of two isomeric allylic chlorides 30 (a/)3 = 3 1) in 68% yield (Scheme 11). The addition of the carbon and chloride across the diene proceeds completely in a stereoselective manner and only the l,4-5yn-addition products are obtained. 

Xie and Qiu have reported the first example of the [2+2+2] carboannulation of arynes, activated alkenes, and arynes. Whereas Pd catalysts promote the two-component benzyne-alkene-benzyne cyclization, under Ni catalysis the three-component reaction is favored leading to 1,2-dihydronaphthalenes 108 from readily available materials. In this case, the catalytic cycle is likely initiated by oxidative coupling of aryne and alkene on Ni to form a nickelacycle that undergoes subsequent insertion of the alkyne into the Ni-C(aryl) bond to give a seven-membered intermediate (Scheme 12.54) [95]. 

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