Dienes, heteroannulation

Larock extended this Pd-catalyzed diene heteroannulation to other dienes and anilines [399], including functionalized dienes leading to, for example, ketotetrahydrocarbazoles [400]. Back has employed 1-sulfonyl-l,3-dienes in this 2-vinylindoline synthesis [401], and the use of 1,3-dienes in constructing indolines has been adapted to the solid phase by Wang [402]. Interestingly, Larock has shown that the electronically-related vinylcyclopropanes undergo a similar cyclization with o-iodoanilines to form 2-vinylindolines, e.g., 310 [403, 404]. Vinylcyclobutane also reacts in a comparable manner. 

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],... 

Carbo and heteroannulation of 1,2-, 1,3-, 1,4-dienes, vinyl cyclopropanes, vinyl cyclobutanes catalyzed by arylmercury, thallium or palladium. 

Back TG, Pandyra A et al (2003) Regiochemical switching in Diels-Alder cycloadditions by change in oxidation state of removable diene sulfur substituents. Synthesis of carbazoles by sequential heteroannulation and Diels-Alder cycloaddition. J Org Chem 68 3299-3302... 

Dieck reported preparation of the tetrahydrocarbazole 337 by heteroannulation of o-iodoaniline with 1,3-cyclohexadiene [137], As a recent example, heteroannulation of the o-iodoaniline derivative 338 with the conjugate dienyl sulfone 339 afforded the vinylogous 2-sulfonylindoline 340, which was converted to the indole derivative 341 by oxidative dehydrogenation [138]. Pd-catalyzed annulation of 1,3-dienes by o-iodoacetoxycoumain 342 offers a synthetic method for dihydro-furocoumarins. The dihydrofurocoumarin 343 was obtained by the reaction of 342 with 1-phenylbutadiene in 80% yield. After optimization, the uses of Pd(OAc)2,... 

Extension of heteroannulation procedure performed by Larock to other unsaturated compounds such as dienes and aUenes has permitted the synthesis of an important range of different heterocychc compounds. 

Heteroatom-containing aryl iodides react with 1,3-dienes in the presence of a palladium catalyst and an appropriate base to afford a variety of oxygen and nitrogen heterocycles. Mechanistically, heteroannulation proceeds via aryl-and TC-aUylpaUadium intermediates. Similar results have been obtained using either Pd(OAc)2 or Pd(dba)2 as catalysts (Scheme 29). The yield of... 

From a synthetic point of view, intermolecular reactions are more interesting, as a wider variety of substrates is available. In 1990, Larock and coworkers reported a palladium-catalyzed heteroannulation of 1,3-dienes with 2-iodophenols and 2-iodoanilines. Dihydrobenzofurans and indolines were isolated in moderate to good yields (Scheme 2.45). In addition to the 2-iodophenols and 2-iodoanilines, 2-iodobenzyl alcohol and 2-iodoben l amine could be applied as substrates as well and gave the corresponding six-membered heterocyclie eompounds as the terminal products. 

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