On Stevens' tropolone synthesis; hydrolysis of spirocyclopentadiene– and spiroindene–dichloroketen adducts

Abstract

Hydrolysis of the spiro[2.4]hepta-4,6-diene–dichloroketen adduct (2a) gave 3-(2′-acetoxyethyl)-1H-cycloheptatrien-1-one (3a) and dihydro-8H-cyclohepta[b]furan-8-one (4a), of which the former was the precursor to the latter. 1-Methylspiro[2.4]hepta-4,6-diene– and spiro (cyclopropane-1,1′-[1H]-indene)–dichloroketen adducts, (2b), (2c), and (6), gave similar results.

The spiro[4.4]nona-1,3-diene–dichloroketen adduct (10) gave spiro[4,6]undeca-8,10-diene-6,7-dione (14), 6-hydroxy-1,2,3,4-tetrahydro-5H-benzocyclohepten-5-one (15) and -7H-benzocyclohepten-7-one (16), and 5-acetoxy- and 5-hydroxy-7-chlorospiro(bicyclo[3.2.0]hept-2-ene-4,1′-cyclopentane)-6-ones, (12) and (13). The spiro (cyclopentane-1,1′-[1H]-indene)–dichloroketen adduct (19) gave similarly spiro (5H-benzocycloheptene-5,1′-cyclopentane)-6,7-dione (22).

The formation of these compounds, especially the seven-membered ring, can be explained by the application of Bartlett's mechanism to Stevens' tropolone synthesis.