A route to a wide range of cyclopentanecarboxylic acids via 4-substituted camphors

4-Carboxycamphor, easily obtainable starting from camphor, is used as a versatile precursor in high-yielding syntheses of a wide range of cyclopentanecarboxylic acids using just a few steps. Regioselective bromination of 4-carboxy- and 4-methoxycarbonyl-3-bromocamphors leads to 10-bromomethyl derivatives in good yields. Grob-type fragmentation reactions proceed smoothly for 10-bromocamphor-4-carboxylic acid, 10-bromocamphorquinone-4-carboxylic acid and 3,4-dibromocamphor with the formation of unsaturated cyclopentanecarboxylic acids. Detailed studies of bromination and rearrangement reactions of brominated camphor-4-carboxylic acid and its derivatives, reported herein, highlight the unique chemistry of substituted camphor and offer easy access to a wide range of 2,2-dimethyl-3-methylenecyclopentanecarboxylic acid derivatives.