Studies in the cycloproparene series: chemistry of 1-acyl-1H-cyclopropa[b]naphthalenes and synthesis of cyclopropa[b]naphthalenylidene enol ethers

The 1H-cyclopropa[b]naphthalenyl anion reacts with N,N-dimethylamides to pr ovide C-l acyl derivatives in good yield in what are rare examples of mono- substitution in the cycloproparene series. The availability of these acylcy cloproparenes provides for subsequent benzylic proton abstraction and enola te ion interception to give O-silyl and O-phosphinate derivatives. This rea ction sequence leads to the first cyclopropa[b]naphthalenylidene enol ether s and provides the only example of exocyclic alkene formation taking place in one step from the benzylic centre. Protonation of the acyl derivatives b y mineral acid triggers three-membered ring opening to 2,3-disubstituted na phthalenes rather than 2-monosubstituted analogues that typically arise fro m protonation at the aromatic ring. Upon thermolysis ring expansion to a na phthofuran occurs. (C) 2001 Elsevier Science Ltd. AH rights reserved.