Boronate titanium alkylidene reagents for diversity-based synthesis of benzofurans.
[reaction: see text] Novel titanium benzylidenes (Schrock carbenes) bearing an arylboronate group are generated from thioacetals with low valent titanium species, Cp(2)Ti[P(OEt)(3)](2), and alkylidenate Merrifield resin-bound esters to give enol ethers. Treatment with 1% TFA gives 2-substituted (benzo[b]furan-5-yl)boronates, and solid-phase Suzuki cross-coupling gives 2,5-disubstituted benzofurans. Steps in the syntheses of thioacetal substrates include selective lithiation-boronation, hydrolysis of a MOM group without affecting a boronate ester, and cross-coupling with bis(pinacolato)diboron.
Department of Chemistry, University of Glasgow, Glasgow G12 8QQ, Scotland.
Gordon J
GJ
McKiernan
Richard C
RC
Hartley