Dehydrogenative nucleophilic addition of aliphatic ether to benzaldehyde dimethyl acetal mediated by ether-boron trifluoride (1/1) affording 1-alkoxy-2-alkylindenes or α,β-unsaturated carbonyl compounds specifically

Article abstract of DOI:10.1246/bcsj.79.627

The R₂O·BF₃-mediated dehydrogenative crossed aldol condensation reaction of acyclic aliphatic ethers with benzaldehyde dimethyl acetal to give specifically indene derivatives or α,β- unsaturated carbonyl compounds has been found. When the ethers have bis(β-alkylethyl) ether structures, dehydrogenative formation of enol ether equivalents followed by successive crossed aldol addition to acetal-originated electrophile and intramolecular electrophilic aromatic substitution reactions give annulation products of 1-alkoxy-2-alkylindenes. When the ether has two β- and one or more α-hydrogens, α,β-unsaturated carbonyl compounds are obtained. The structural correlation between deuterated starting materials and the obtained products, the structural requirements for ethers, and the distinct substrate specificity have revealed the reaction routes and mechanisms.