Acid-catalysed intramolecular C-alkylation in βγ-unsaturated diazomethyl ketones. A new synthetic route to angularly fused cyclobutanones, bridged cyclopentanones, and γ-lactones
Acid-induced decomposition of rigid polycyclic βγ-unsaturated diazomethyl ketones (2a and b) and (4a and b) is shown to give, in excellent yields, the respective angularly fused unsaturated cyclobutanones (5a and b) and (6a and b) and/or the rearranged bridged hydroxycyclopentanones (7a) and (9a) depending upon the reagents, reaction conditions, and the nature of the substrates. Under certain conditions (5a) and (7a) undergo rearrangement to 3a-methyl-1,2,3,3a,6,7-hexahydropentaleno[1,6a-a]naphthalen-4-one (12a). The unsaturated cyclobutanones undergo stereoselective catalytic hydrogenation to the respective trans-angularly substituted hydrophenanthrene and hydrofluorene cyclobutanones (13a and b) and (14a and b) which on facile Bayer–Villiger oxidation produce the γ-lactones (18a and b) and (19a and b). The unsaturated cyclobutanones (5a and b) also afford the respective γ-lactones (20a and b) on oxidation with alkaline hydrogen peroxide.