Dienes trifluoromethylation, olefin

As has been noted already in Section IV.B.3, Smart and Middleton103 generated bis(trifluoromethyl)sulfene (126) in solution by treating [(Me2N)3S + C(CF3)2S02F with silicon tetrafluoride or boron trifluoride. This sulfene adds to various dienes and olefins to give [4 + 2] and [2 + 2] adducts in moderate to good yields (equations 113-117). 

Hanzawa Y, Kawagoe K, Kimura N, Kobayashi Y. Stereoselective synthesis of trifluoromethylated olefin and diene. Chem. Pharm. Bull. 1986 34 3953-3955. 

The phosphonium salt method works best with nucleophilic olefins [//, 12, 16, 17, 18, 19] (Table 1 and equations 1-3) and has been used m mechanistically important studies of difluorocarbene additions to norbornadienes [20 21, 22, 23] that provided the first example of a concerted homo-l,4-addition (equation 4) A recent modification uses catalytic 1,4,7,10,13,16 hexaoxacyclooctadecane (18-crown-6) to shorten reaction times and increase yields with less nucleophilic olefins [12] (Table 1) Neither procedure, however, compares with the use of phenyl(tri-f1uoromethyl)mercury or (trifluoromethyl)trimethyltin reagents [efficient reactions with less nucleophilic olefins (equations 3 and 5) and cyclic dienes [24, 25] (equations 6 and 7)... 

Certain 1,5 diazabicyclo[3 3 0]oct-2-enes can be transformed unexpectedly into 4//-5,5-dihydro-l, 2 diazepines on heating [209] 1,5-Dipoles formed on heating of l,5-diazabicyclo[3 3 0]oct-2-enes [210] can be trapped with olefins to give [3+2] cycloadducts At elevated temperatures, they undergo a [3+2] cycloreversion Tins reaction sequence offers a simple route to dienes with interesting substitution patterns, for example, 1,1 bis(trifluoromethyl)-l,3-butadiene [211] The [3+2] cycloadducts that arise from the reaction of the 1,5 dipoles with acetylenes undergo... 

Next, some reactions of hexakis(trifluoromethyl)benzvalene will be discussed. This compound is very stable as mentioned before and its olefinic double bond reacts as an efficient dienophile. The difference in the reactivity between unsubstituted benzvalene and the hexakistrifluoromethylated derivative is that the former is nucleophilic while the latter is highly electrophilic. Thus, the former does not react with usual 1,3-dienes, in contrast to the latter. Here, mainly describe our results of the several reactions of hexakis(trifluoromethyl)benzvalene which were designed for the synthesis of tetrakis(trifluoromethyl)tetrahedrane. 

The Diels-Alder reaction of hexakis(trifluoromethyl)benzvalene with furan had been reported 63) but not its stereochemistry. We have examined this reaction and found that it proceeds smoothly with many 1.3-dienes if the steric requirement of the olefin is not large in the transition state where exo-attack occurs as confirmed by X-ray analysis (97)96). Therefore, 2,3-dimethylbutadiene reacts smoothly with hexakis(trifluoromethyl)benzvalene whereas 1,3-pentadiene reacts very slowly and 2,4-hexadiene does not at all. The cycloaddition to cyclobutadiene gives a mixture of endo- and exo-adducts (98)97) ... 

The first hving polymerization of cyclic olefins with a high ring strain [28], such as norbomenes, norbornadienes (bicyclohepta-2,5-dienes, NBDs) or the Feast-monomer 7,8-bis(trifluoromethyl)tricyclo[4.2.2.0 ]deca-3,7,9-triene (TCDTFj) by W(N-2,6 i Pr2 C6H3)(CH- Bu)(OCMe(CF3)2) [34] was re-... 

Free-radical initiation of the polymerization of pcrfluorobut-2-yne is difficult, and the solid polymer has previously been obtainable only by y-ray initiation or by a fluoride-initiated anionic pathway. - " A new technique now disclosed involves the use of trifluoromethyl hypofluorite, which at sub-ambient temperatures catalyses the conversion of the butyne to a polymer which is quite stable at 450 "C. Mass spectrometric analyses of the oligomers obtained by the anionic pathway, containing up to twelve butyne units, are consistent with an all-fra s conjugated polyolefin structure H—[CfCFs) C(CFa)]B—F. This result is wholly consistent with trapping experiments in which the incipient vinyl anions are intercepted by, for example, penta-fluoropyridine to give /ranj-olefins and /ranj,fra j-dienes. - ... 

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