The potential generality of a two-step formylation–cyclisation reaction of a few rigid β,γ-unsaturated methyl ketones as a route to some functionalised, angularly fused cyclopentenone and cyclopentanone derivatives has been examined. Thus, perchloric acid-catalysed reaction of the β-diethoxyethyl ketones (4a–c) and (4d) derived from the 1-acetyl-1-methylhexahydrophenanthrenes (1a–c) and 1-acetyl-1-methyltetrahydrofluorene (1d) afforded the corresponding angularly fused styrenoid cyclopentenones (2a–c) and (2d) in good yields. Under similar conditions, the methoxytetrahydrofluorene analogue (4e) produced 1-methyl-7-methoxyfluorene (11). While repetition of the reaction of the β-diethoxyethyl ketones (4a) and (4c) with perchloric acid in the presence of triethyl orthoformate produced the respective pentacyclic pyranocyclopentanones (3a) and (3c) in excellent yields, the p-methoxystyrenoid ketone (4b) gave the cyclopentenone (2b). The carbonyl-conjugated double bond in the dienones (2a–c) undergoes chemoselective catalytic hydrogenation using piperidine and palladium–charcoal, affording the respective styrenoid cyclopentanones (16a–c). The methoxycyclopentanone (16b) has been transformed to the tetracyclic keto phenol (17), representing a highly degenerated estrone molecule.