Oxidations of allethrolone (1a) and naturally derived pyrethrolone (1d) with manganese dioxide under controlled conditions give the corresponding diones (2a) and (2d), respectively. Under more vigorous conditions oxidation of (1a) and (1d) leads to the novel tetraone dimers (3) and (8) respectively. Dimer (3) can also be obtained from dione (2a) by oxidation with manganese dioxide.Cinerolone (1b) and jasmololone (1c) are similarly oxidised to the corresponding diones (2b) and (2c), by manganese dioxide, but do not appear to give tetraone dimeric products.