A highly selective intramolecular trans-silylvinylation of internal alkynes catalyzed by RuHCl(CO)(SIMes)(PPh3) has been accomplished. The use of methyl vinyl ketone as an additive increased the efficiency of this transformation. This process was used to successfully form five-, six-, and seven-membered oxasilacycles by a formal anti-exo-dig cyclization.
The intramolecular trans-silylruthenation of internal alkynes and subsequent insertion of vinyl boronates is described. This approach provides complete regiocontrol through a stereoselective trans-5-exo-dig cyclization which affords a tetrasubstituted olefin as a vinylsilane and a highly functionalized Z,E diene motif.
The cycloisomerization of vinyl silicon-tethered 1,7-enynes has been accomplished using catalytic Cp*Ru(COD)Cl. The products possess a new silane moiety and trisubstituted alkenes as part of the diene system. The reaction scope includes aryl, alkyl, vinyl, and cyclopropyl alkyne functionalities. Silicon was found not to be a mandatory component of the tether. The utility of the products was demonstrated through manipulation of the vinyl silane and Diels-Alder chemistry.
Imidazo[4,5-c]pyridines were synthesized in three steps utilizing a palladium-catalyzed amidation/cyclization strategy. N-Aryl substrates were synthesized using copper-catalyzed amidation of 3-amino-N-Boc-4-chloropyridine. Complementary protocols for the selective chlorination of imidazo[4,5-c]pyridines at the C2 and C7 positions were also developed.
b]pyrazines using a palladium-catalyzed amidation that utilizes Xantphos as an ancillary phosphine ligand is reported. The use of a binary solvent system comprised of 1,4-dioxane and tert-amyl alcohol was crucial in eliminating unwanted by-products.
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