Abstract
Cycloaddition of tungsten-η 1 -3-furyl compounds with a variety of organic alkenes and alkynes proceeds smmothly at ambient conditions, yielding tungsten-η 1 -oxabicyclo[2.2.1]-heptene and -η 1 -oxabicyclo[2.2.1]heptadiene compounds in high regioselectivities and stereoselectivities. The cycloaddition is proposed to proceed via a mechanism involving a zwitterion intermediate. Cleavage of oxygen bridges of η 1 -oxabicyclo[2.2.1]heptenes and η 1 -oxabicyclo[2.2.1]heptadienes occurs on treatment of CF 3 SO 3 H and Lewis acid, leading to atypical carbon-carbon bond scission and deoxygenation reactions to give highly substituted benzene and furan derivatives, respectively. The role of the tunsten fragment in these demetalation reactions is discussed in detail.