Original syntheses of carbonyl compounds and gem-dihalocyclopropanes from β-hydroxyalkylselenides

β-hydroxyalkylselenides possessing two alkyl substituents on the carbon bearing the selenenyl moiety react with dihalocarbenes generated from haloforms and thallous ethoxide or under phase transfer catalysis to produce ring enlarged ketones as the sole product in the first case, as the main product in the second. The reaction takes another course when the dihalocarbenes generated from haloforms and tBuOK or from trihalomethylphenylmercury are employed and leads inter alias to dihalocyclopropanes.