An efficient Pd-catalyzed domino reaction of α,α-dialkyl-(2-bromoaryl)methanols to 6,6-dialkyl-6H-benzo[c]chromenes is presented. Their formation can be explained via a five membered Pd(II)-cycle that efficiently involves a domino homocoupling with the second molecule, β-carbon cleavage, and finally intramolecular Buchwald-Hartwig cyclization. This domino process effectively involves breaking of five σ-bonds (2C-Br, 2O-H, and a C-C) and formation of two new σ-bonds (C-C and C-O). This mechanistic pathway is unprecedented and further illustrates the power of transition metal catalysis.
Lewis acid (FeCl3) mediated dual bond (C-C and C-O) formation for synthesis of 3,4-dihydrocoumarins is presented. This method has successfully delivered a number of dihydrocoumarins containing dense functionalities on the aromatic ring. Significantly, the present method enabled achieving dihydrocoumarins with tertiary as well as quaternary carbon atoms at the benzylic position. Gratifyingly, the novel spiro-tetracyclic lactones have also been dextrously prepared using this process.
Am ild andp ractical method is developed for the efficient synthesis of (1,1-dimethyl-3-phenylbut-3-enyl)benzenes and indanes promoted by Lewis acid, startingf rom tert-benzyl alcohols. The reactioni st emperature dependent and furnished the products with excellentr egioselectivity.I n the case of simple dimerization, Markovnikov head-to-tail coupling took place. On the other hand, reactiona te levated temperatures gave indanes throughs ubsequentF riedel-Crafts cycloalkylation.S ignificantly,e ven electron-rich aromatic systems were compatible for the formation of indanes, which would not be feasible by earlier reports,t hus, revealing the advantage of the mild nature of the present protocol.[a] Assoc.
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