Stereochemistry of some olefins RfCH=CHI and the preparation of some new cyclopropenes

Abstract

The light induced additions of CF3I and C2F5I to acetylene yield the trans 1:1 adducts predominantly [CF3CH=CHI (trans:cis = 6.7:1) and C2F5CH=CHI (trans:cis = 9:1)]. The addition of i-C3F7I to acetylene gives a 1:1 adduct consisting of a higher proportion of the cis isomer (trans:cis = 1.78:1). The i-C3F7I-acetylene adduct can be dehydrohalogenated to produce i-C3F7C≡CH. Difluorocarbene (from (CH3)3SnCF3) does not add to the olefinic 1:1 adducts but does add to the polyfluoroalkyl acetylenes RfC≡CH to produce the cyclopropenes [Formula: see text]