Difluoroallylation

Difluoroallyl)trimethylsilane Silane, (3,3-difluoro-2-propenyl)trimethyl-(9) (40207-81-6)... 

Radical addition of dibromodifluoromethane to alkenes followed by sodium borohydride reduction is a convenient two-step method for the introduction of the difluoromethyl group.5 Either one or both carbon-bromine bonds in the intermediate dibromides may be reduced, depending on the reaction conditions. In the case of acyclic dibromodifluoromethane-alkene adducts, the reduction occurs regioselectively to yield the relatively inaccessible bromodifluoromethyl-substituted alkanes. The latter are potential building blocks for other fluorinated compounds. For example, they may be dehydrohalogenated to 1,1-difluoroalkenes an example of this methodology is illustrated in this synthesis of (3,3-difluoroallyl)trimethylsilane. 

Difluoroallyl)silanes are of interest as carbon-carbon bond forming building blocks in organofluorine chemistry,4 7>8... 

J. Gonzalez, M. J. Foti, and S. Elsheimer 225 (3,3-DIFLUOROALLYL)TRIMETHYL- SILANE... 

Starting from Difluoroallylic and Difluoropropargylic Derivatives Just like the esters of bromodifluoroacetic acids, difluoroallylic and difluoropropargylic bromides (via organometallic derivatives) can add onto aldehydes and couple with activated halides (Figure 2.17). ... 

Bromo-3,3-difluoropropene reacted with -butyl lithium in the presence of carbonyl compounds or trialkylsilyl chloride to give the corresponding a,a-difluoroallylic derivatives. The difluoroallyllithium was proposed as an intermediate [280-282] (Scheme 96). 

In the presence of zinc, cadmium or tin, 3-bromo-3,3-difluoropropene also reacted with carbonyl compounds to give the a,a-difluoroallylic alcohols in good yields [283] (Scheme 97). 

Treatment of difluoroallylic alcohols with sulfur(II) or phosphorus(III) halides resulted in [2,3]-rearrangement (Eq. 135) under mild conditions [349]. This method constitutes a potential alternative route to difluorophosphonates, and to difluorosulfoxides and sulfones. The Jussieu group showed that thionyl chloride or bromide converted difluoroallylic alcohols to the corresponding halodi-fluoromethyl allylic compounds (Eq. 136) [350]. Exposure to DAST afforded the trifluoromethyl congeners [351, 352] and Kumadaki showed that /i-chloro-y,y-difluoroallylic alcohols afforded the trifluoromethyl alkene products upon treatment with HF. 

Carbenoid additions to y,y-difluoroallylic compounds represent valuable methodology complementary to the difluorocarbene chemistry described in Sect. 2.1. One example was provided by Boger and Jenkins [353] at Scripps during a synthesis of a duocarmycin analogue. Intramolecular rhodium-catalysed carbenoid addition of a p-quinonediazide to a protected difluoroallylic amine formed a key intermediate (Eq. 137). 

Reductive defluorination reactions have also been described in ether, difluoroallylic alkoxides undergo stereoselective reduction (Eq. 138) to the E-mono-fluoro derivatives upon treatment with lithium tetrahydridoaluminate [354]. Sodium borohydride [355] and Red-Al [346] have also been used to achieve this transformation. 

The preference for the methyl group to assume an equatorial orientation is presumably reinforced by the necessity to avoid a 1,3-diaxial repulsion with the axial hydroxyl group. Similar routes to monofluorocyclohexanes [378] and difluorocyclopentanes [379] have been described by these authors. Recently, difluoroallylic radicals were investigated (Eq. 153) products from 6-exo and... 

Table 7. [2,3] Wittig Rearrangement of 3.3-Difluoroallyl Ethers 23 to Highly...

Difluoroallyl propionate 1 is reported to rearrange to 3,3-difluorohex-4-enoie acid 2 in 57% yield.17... 

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