| Abstract
| - Titanium(IV) benzylidenes bearing a masked oxygen or nitrogen nucleophile in the ortho positionwere generated from thioacetals, using low-valent titanocene complex, Cp2Ti[P(OEt)3]2. Methyleneacetal, alkyl ether, silyl ether, fluoro, tertiary amino, and N-alkyl, N-benzyl, N-prenyl, and N-silyltert-butyl carbamate groups were tolerated in the titanium alkylidene reagents (Schrock carbenes).Aryl−chlorine bonds were stable to the titanium benzylidene functionality, but there was poorchemoselectivity for the reduction of the thioacetal in the presence of an aryl chloride. The titaniumbenzylidenes converted Merrifield and Wang resin-bound esters into enol ethers. The oxygennucleophile was masked as a TMS ether, and when the resin-bound enol ethers bearing this orthosubstituent were treated with 1% TFA in dichloromethane, benzofurans were released from resinin high yields. The chameleon catch strategy ensured excellent purity. In a similar way, N-alkylatedand N-silylated tert-butyl carbamates were used for the synthesis of N-alkyl and N-Boc indoles,respectively. These traceless solid-phase syntheses of heterocycles are believed to involve postcleavage modification rather than cyclative termination.
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