Magnesium trifluoromethyl derivatives

Phenyl trifluoromethyl ketone has been used as a standard for comparing stereoselectivities in Meerwein-Ponndorf-type reductions with chiral alkoxyalu-minium and magnesium halides derived from monoterpenoid alcohols, and (24) is one of the few to show high selectivity (77% enantiomer excess). The alkylative addition of butyl-lithium to aldehydes in chiral media has been studied as part of a general programme to develop auxiliaries, based on tartaric acid, for asymmetric synthesis. Optical yields of up to 40% in the butyl carbinol products are obtained at low temperature in solutions containing chiral 1,2-dihetero-ethane derivatives such as (25), which are believed to complex the alkyl-lithium as in (26). 

Trifluoromethyl)-2-(2-chloro)ethoxy-l-bromoethane (3-Trifluoromethyl)phenyl magnesium bromide is prepared under the normal conditions for magnesium derivatives, from 48.6 g of magnesium turnings and 455.7 g of (3-trifluoromethyl)bromobenzeneand 1.5 liters anhydrous ether. 

Trifluoromethylation of pyrrole (and indole and imidazole) occurs on irradiation of a mixture of the compound with difluorodiiodomethane, again via a SET mechanism involving fragmentation of the radical anion (Scheme 31). The presence of the CF3 group in the final products, 45 and 46, is a result either of secondary decomposition of the initially formed—but not isolated—difluoroiodomethyl derivatives, or of formation of the CF3 anion or radical in situ [94], Perfluoroalkyla-tion of pyrroles can also be achieved by an SrnI mechanism—by reaction with perfluoroalkyl iodides in the presence of magnesium or zinc [95]. Indole, on the other hand, gives a mixture of the seven possible alkylated derivatives when irradiated in the presence of ethyl chloroacetate [96],... 

X-(Trifluoromethyl)ethenyl boronic acid (72) was conveniently prepared from the reaction of readily available 2-bromotrifluoropropene with alkyl borate and magnesium in one-pot. The Suzuki coupling of 2-amino-3-methoxy-5-bromopyrazine (71) with boronic acid 72 provided styrene derivative, 73 in excellent yield [43]. 

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