Silyl Migrations of Various 3 " [ ( Trialkylsilyl ) - Oxymethyl ] - Furans and - Thiophenes

That 3-[(t-butyldimethylsilyl)oxymethyl]furan 1_ can be lithiated at C-2 (n-BuLi/ether/r.t./6hj and the resulting anion quenched with electrophiles is well known. Treatment of the above anion with 1-bromo-3-chloropropane result ed in a poor yield of 2_; however, changing the reaction conditions (n-BuLi/THF 0°C/6h) and then adding HMPA with the electrophile resulted in the isolation o 1 (h0% by H NMR) and 2-(t-butyldimethylsilyl)-3"(hydroxymethyl)furan 3̂ (60$ by H NMR) (Scheme 1 ) . That the silyl group was indeed at C-2 was confirmed b treating 4_ with 2.2 equivalents of n-butyHithium and quenching the resulting anion with 1.0 equivalent of t-butyldimethylsilyl chloride; the spectral data of 3_ prepared from both 1_ and 4_ were identical. As 1,4 0-»C silyl migrations are rare we decided to investigate this unexpected result. Optimized results were obtained by treating l_ with 1.1 equivalents of n-BuLi in the presence of HMPA in either THF or DME at -20°C for 1 hour to produce :3_ in 87% yield. This silyl migration turned out to be a general SCHEME 1