The Lewis acid promoted reaction of 1,1-diarylallenes with ketone derivatives was
examined. The tin(IV) chloride promoted reaction of diarylallenes with vinyl ketones
gave indene derivatives through a conjugate addition/cyclization reaction. The reaction
of diphenylallene with diethyl oxomalonate in the presence of one equivalent of tin(IV)
chloride at –40 °C gave diethyl hydroxy(3-phenyl-1H-inden-2-yl)malonate as the major product through a carbonyl addition/cyclization
reaction, whereas the same reactants in the presence of 0.2 equivalents of tin(IV)
chloride at 80 °C gave diethyl (3-phenyl-1H-inden-2-yl)malonate. Diethyl hydroxy(3-phenyl-1H-inden-2-yl)malonate was also converted into the latter product on heating at 80 °C
in the presence of 0.2 equivalents of tin(IV) chloride.
Key words
allenes - Lewis acids - ketones - cyclizations - Michael additions - addition reactions