BF3-promoted cyclization reaction of imines and salicylaldehyde with silyl enol ethers:: unexpected formation of dioxaspiro compounds

Unexpected spiro cyclic products were formed from the reaction of imines and salicylaldehyde with silyl enol ethers in the presence of BF(3.)OEt(2). Different kinds of dioxaspiro products were afforded depending on the nature of starting materials. Furthermore, salicylaldehyde could also react directly with several silyl enol ethers. giving three products with different spiro cyclic structure Under the same reaction conditions. (C) 2008 Elsevier Ltd. All rights reserved.