Allene heteroannulation

Scheme 7-10 A proposed reaction path of Pd-catalyzed carboylative heteroannulation ofo-iodothiophenol with allene...

Undoubted, 2-haloaniline derivatives still maintain most vored precursor status for the preparation of the indole nucleus. Larock now reports the frill details of his examination of the asymmetric addition of IV-tosyl-2-iodoaniline (63) to allenes 64 (e.g. 1,2-undecadadiene) in the presence of palladium catafysts and chiral bisoxazoline ligand to afford chiral indolines 65 in up to 88% ee <99JOC7312>. Cook has utilized the palladhjm-catafyzed heteroannulation of iodoanilines with alkynes derivatized with the Schollkopf chiral auxiliary as a reliable route to optically active ring-A substituted tryptophans <99TL657>. 

The highly reactive 2-azadiene with an allene and heterocumulene structure 126, prepared by gas-phase thermolysis of propargyl thiocyanate, has been found by the Banert group to be an efficient precursor for thiazole derivatives by nucleophilic-induced heteroannulation through carbon and... 

The palladium-catalyzed ring heteroannulation of allenes 278 by tosyl amide and amine-containing allyl and vinyl halides (e.g., 277) provided a facile route to a variety of azepanes (e.g., 279) (Equation 39) <2003JOC6859> in the case of iV-tosyl-(2-iodophenyl)ethylamine, benzazepines are formed. 

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],... 

Allenes undergo a Pd-catalyzed regioselective carbonylative heteroannulation with 2-iodothiophenols and carbon monoxide and this offers an attractive route to 3-methylene-thiochromanones 546 (Equation 198) <1999JOC9646>. 

Palladium-catalyzed heteroannulation is illustrated by synthesis of substituted l//-benzo[rf]azonine 227, which was prepared from allene and tosylamide-containing aryl halide (Equation 26). The reaction was suggested to proceed by addition of an arylpalladium compound to the allene to generate a 7i-allylpalladium intermediate, which subsequently undergoes nucleophilic displacement of palladium at the less-hindered end of the 7i-allyl system <1998JOC6859>. 

Alper and Xiao [45] synthesized thiochromanones by palladiumotalyzed carbonylative ring-forming reactions of 2-iodothiophenol derivatives, allenes, and CO. The fhiochroman-4-ones were achieved in good to excellent isolated yields with high regioselectivity, which was probably caused by electronic effects (Scheme 1.24). This catalytic heteroannulation comprises the regioselective addition of the sulfur moiety on the more electrophilic carbon center of the allene, arylpalladium formation, CO insertion, subsequent intramolecular cydization, and, finally, the reductive elimination. 

In 1999, Alper and Xiao developed a novel access to thiochroman-4-one derivatives by palladium-catalyzed carbonylative heteroannulation of o-iodothiophenols with allenes. The reaction afforded the thiochroman-4-ones in good to excellent isolated yields with high regioselectivity (Scheme 3.76). The catalytic heteroannulation may involve regioselective addition of the sulfur moiety of the reactants on the more positive end of the allene, atylpalladium formation, CO insertion, subsequent intramolecular cyclization, and then reductive elimination. 

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