Abstract The chlorocarbenes 2, generated thermally from the diazirines 8, take part in [2+ 1]- cycloaddition reactions with the phosphaalkenes 5 to furnish the dichlorophosphiranes 9. At 130 C, the latter products 9 undergo elimination of chlorotrimethylsilane to form the 1-chloro- 1 Full-size image (< 1 K)