A formylation-cyclisation method of synthesis of cycloalkenones from unsaturated ketones. Part 3. Simple synthesis of some functionalised angularly fused cyclopentenone and cyclopentanone derivatives

Abstract

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 ρ-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.