Dihalocarbenes have been generated mainly by thermal decomposition
of sodium trihaloacetate and phenyl (trihalomethyl)mercury,
and give gem-dihalocyclopropyl adducts with various steroid olefins.
A new procedure involving the use of sealed tubes makes possible the
addition of dihalocarbenes to sterically hindered olefins. In this manner,
7-cholestenyl benzoate when treated with PhHgCC1₃...