Arenecarbaldehyde dimethylhydrazones were successfully acylated by trifluoroacetic anhydride to afford trifluoroacetylated hydrazones 2. Several 5-Aryl-6-trifluoromethyl-3,6-dihydro-2H-1,3,4-oxadiazines 3 were synthesized in good yields by novel cyclization of 2, thus obtained, using silica gel as an effective catalyst. Hydrolytic ring cleavage of 3 afforded α-hydroxyketones 5 bearing the trifluoromethyl group in high yields.
Diketo Compounds with (Trifluoromethyl)trimethylsilane: Double Nucleophilic Trifluoromethylation Reactions
作者:Rajendra P. Singh、Jeffry M. Leitch、Brendan Twamley、Jean'ne M. Shreeve
DOI:10.1021/jo0057304
日期:2001.2.1
Reactions of various diketo compounds with (trifluoromethyl)trimethylsilane (Me3SiCF3) in the presence of catalytic amounts of cesium fluoride have been studied. gamma -Ketoesters, CH3COCH2CH2CH2R (R = Et, Bu), were reacted with 2 equiv of Me3SiCF3 at room temperature to give CH3C(OH)(CF3)CH2CH2COCF3 in good yield after hydrolysis. alpha -Diketones, R1COCOR2 (R-1 = R-2 = Ph; R-1 = Ph, R-2 = Me; R-1 = R-2 = Me; R-1 = Me, R-2 = Et), when reacted with Me3SiCF3, formed 1:1 or 1:2 addition products depending on the reaction conditions and stoichiometry used. Reactions of diones CH3COXCOCH3 (X = -CH2CH2-, -C6H4C6H4-, -CH2-) with Me3SiCF3 also led to the formation of the mono- or diaddition products depending on reaction conditions. With various kinds of substituted arylglyoxals, 2 equiv of Me3SiCF3 produced monoaddition products in 70-75% yield and diaddition products in 5-10% yield. One of the monoalcohols and two of the diols have been characterized by single-crystal X-ray analysis, and the presence of inter- and intramolecular hydrogen bonding has been confirmed.
Facile synthesis of aromatic unsymmetrical fluorine-containing acyloins through the reductive trifluoroacetylation of benzaldehyde and transposition of the carbonyl group
The reductive coupling reaction between benzaldehyde and ethyl trifluoroacetate in the presence of magnesium and chlorotrimethylsilane in N-methyl-2-pyrrolidinone gave the acetal of the corresponding coupling compound in good yields. The yield of the coupling product largely depended on the benzaldehyde concentration in the solution and it was essential to avoid the formation of pinacol type compounds