Stereochemistry of some olefins R_fCH=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]

Preparation and properties of some fluorocarbon derivatives of tin

“…The compound (CH3)3SnCH(CF3)2 was obtained by treating (CH3).3SnH with (CF3)2CN2. 23 The chemical shifts and coupling constants from the 19F nmr spectra of the new compounds are similar to those of other derivatives containing an Rf group bonded to a main group metal or metalloid.24•26 It is notable that in the fluoroalkyltrimethyltin compounds coupling takes place between the methyl hydrogens and a fluorine atom on the carbon that is ß to the tin but no coupling takes place between the hydrogens and the fluorines attached to the carbon atom that is a to the tin atom. This long-range coupling has been noted before26 and similar even more remote couplings are found in (CH3)3SiRf compounds.…”

“…In all cases a shift to lower field occurs as the size of the Rf group increases. 6 The apparent equivalence of the electronegativities of CF3 and CH(CF3)2 is surprising and it appears that there may be another affect causing an electric field gradient in (CH3)3SnCH(CF3)2. Powell and Lagowski34 have attempted to estimate the electronegativities of various saturated Rf groups but their results are not definitive.…”

ChemInform Abstract: Synthesis of gem‐Difluorocyclopropa(e)nes O‐, S‐, N‐, and P‐Difluoromethylated Compounds with TMSCF2Br.

“…However, a major limitation of most of the difluorocarbene sources is that they focus on only one type of reaction, either [2+1] cycloaddition with alkenes/alkynes under nonbasic conditions (Category A) [12][13][14][15][16][17][18] or a-addition with Nu-H under basic conditions (Category C). [6][7][8][9][10][11] Although difluorocarbene generated from FSO 2 CF 2 CO 2 H [19] and FSO 2 CF 2 CO 2 TMS (TFDA; Category B) [20] under nonbasic conditions is reactive towards both alkenes/alkynes and Nu-H, the synthesis of difluoromethyl compounds with these reagents is subject to low yields [19] or narrow substrate scope.…”

Access to carbon–carbon bonds

“…Applications have included difluorocyclopropanation of steroids 602 and even difluorocyclopropenation of perfluoroalkyl acetylenes 603 . The reac tion has been extended to other dihalocyclopropanations with triorganostannyl trihaloacetates as in situ trihalomethyltin precursors 604 " 606 .…”