Reaction of phase transfer generated dichlorocarbene with 9-thiomethylphenanthrene (4) leads to 6 rather than the expected addition product 5. 6 is formally derived from a carbene insertion into the C,S bond. ¹³C-labelling shows that the CH₃ group of 4 is lost during the reaction. Addition of dichlorocarbene, generated under phase-transfer conditions, to 9-methylthiophenanthrene (4) gives 6 instead of the expected adduct P15.