FULL PAPER DOI: 10.1002/ejoc.200900487 Atom-Efficient Vinylic Arylations with Triarylbismuths as Substoichiometric Multicoupling Reagents under Palladium Catalysis Maddali L. N. Rao,* [a] Deepak N. Jadhav, [a] and Varadhachari Venkatesh [a] Keywords: Arylation / Bismuth / Palladium / Atom efficiency / Cross-coupling The first atom-efficient arylation of vinylic iodides was achieved by using triarylbismuths as substoichiometric multicoupling reagents under palladium catalysis. Vinylic io- dides were efficiently coupled with electronically divergent Introduction The coupling reaction of organic electrophiles with orga- nometallic reagents is highly demanding methodology for natural product synthesis and other applications in organic synthesis. [1] Given their importance in industry, [2] the search for new nucleophilic [3] and electrophilic [4] coupling partners is inevitable to enrich this chemistry for further applications in organic synthesis. With a view to develop a new class of nucleophilic organometallic reagents that can serve in substoichiometric amounts with respect to electrophilic partners, we have unraveled novel and atom-efficient reac- tivity of triarylbismuths [5] for C–C bond formation reac- tions under palladium catalysis. [6,7] Heck arylation is a novel strategy for the synthesis of substituted alkenes. [8] However, arylation of vinylic sub- strates through cross-coupling provides a facile approach for the synthesis of highly substituted alkenes. [9] Further, chemoselective arylation is often a difficult task in the pres- ence of functionalities that are more labile under metal con- ditions. So, development of a task-specific, new catalytic protocol is usually driven by the relative reactivity of the nucleophilic and electrophilic coupling partners. In cross- coupling reactions, this amenability thus depends on the nucleophilic coupling partner and its reactivity under metal-catalyzed conditions. In general, vinylic substrates react efficiently under metal-catalyzed conditions. [9,10] However, the reactivity pro- files of these substrates vary depending on the nature of the leaving groups, such as triflates, bromides, iodides, and phosphonates. This variance in reactivity usually depends on the relative ability of these substrates to oxidatively add [a] Department of Chemistry, Indian Institute of Technology Kan- pur, Kanpur – 208 016, India Fax: +91-512-259-7532 E-mail: maddali@iitk.ac.in Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejoc.200900487. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Org. Chem. 2009, 4300–4306 4300 triarylbismuths to furnish the corresponding arylated prod- ucts in short reaction times. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) to a metal center and their own stability in the presence of a metal catalyst. [11] As a result, vinylic iodides are relatively less studied, as they are more labile in comparison with other vinylic substrates. Recently, vinylic phophonates were used as more-stable coupling partners for Suzuki cross-couplings. [9e] As is well known, vinylic systems are an important class of com- pounds in synthetic organic chemistry. Further, develop- ment of new coupling reactions with vinylic substrates is highly desirable due to their key role in the synthesis of several natural products. [1] In continuation of our interest to develop more efficient cross-coupling reactions under rel- atively mild catalytic conditions, we extended our efforts towards coupling reactions of vinylic iodides with triaryl- bismuths. During these efforts we have indeed found that the cross-coupling of triarylbismuths with vinylic iodides is efficient under palladium catalysis. We report here for the first time the palladium-catalyzed arylation of vinylic io- dides with functionalized triarylbismuths. Results and Discussion In our initial optimization efforts, we investigated the coupling of 4-iodo-1,2-dihydronaphthalene with tri- phenylbismuth under palladium-catalyzed conditions (Table 1). The coupling reaction studied under different conditions revealed that cesium carbonate in N,N-dimethyl- acetamide (DMA) was the right combination to afford good cross-coupling conversion to give 4-phenyl-1,2-dihy- dronaphthalene in short reaction time (Table 1, Entry 9). Other carbonates of sodium, potassium, and barium did not produce respectable conversion in DMA solvent (Table 1, Entries 1–3). Whereas cesium carbonate as base in N-methyl-2-pyrrolidone (NMP) and N,N-dimethylform- amide (DMF) solvents furnished reasonable conversion, the reactivity was poor in THF and 1,4-dioxane solvents (Table 1, Entries 4–7). The coupling reaction carried out at