| A novel metal-catalyzed method for the synthesis of furans from allenyl ketones has been developed. This approach features a 1,2-migration of alkyl- or aryl groups in the allenyl ketones as the key step. This method allows for efficient synthesis of up to fully carbon-substituted and fused furans. Facile cycloisomerization in the presence of cationic complexes, as well as migratory aptitude studies strongly support electrophilic mechanism for this transformation.;Through computational and experimental studies, the mechanisms of Au-catalyzed cycloisomerization of bromoallenyl ketones have been elucidated. It was found that both Au(I)- and Au(III)-catalyzed transformations proceed via cyclic Au-carbenes. A 1,2-Br migration to the carbene center in these intermediates is kinetically favored over a 1,2-H shift. However, the chemoselectivity of the Au(I)- and Au(III)-catalyzed reactions toward 1,2-H- or 1,2-Br migrations is ligand-dependent.;A mechanism of the Au-catalyzed cycloisomerization of propargylpyridines has been investigated. Both DFT computational and experimental results support an alternative mechanism involving a Au-carbene intermediate over the previously proposed path featuring Au-vinylidene species. For the beta-Si-substituted Au-carbene, the 1,2-Si migration was shown to be kinetically favored over the 1,2-H shift.;A novel efficient regiodivergent Au-catalyzed cycloisomerization of silyl-substituted allenyl- and homopropargylic ketones into 2- and 3-silylfurans has been developed. This cascade transformation features 1,2-Si- or 1,2-H migrations in a common Au-carbene intermediate. The 1,2-Si migration is kinetically favored over 1,2-shifts of H, alkyl, and aryl groups in the beta-Si-substituted Au-carbenes. However, certain counterion and solvent effects could reverse this migratory preference.;A novel Au-catalyzed cascade cycloisomerization of propargylic esters leading to unsymmetrically substituted naphthalenes has been developed. This cascade process involves a sequence of 1,3- and 1,2-migrations of two different migrating groups. It is believed that this transformation proceeds via a formation of 1,3-diene intermediate, which, upon carbocyclization and aromatization steps, transforms into the naphthalene core. In addition, a variety of 1,3-dienes could be accessed stereoselectively via a 1,3-migration-proton transfer cascade. |
