and commercially available at a reasonable cost.6 Trifluor-
oacetaldehyde ethyl hemiacetal has been used for the synth-
esis of a wide variety of trifluoromethylated compounds such
as β-hydroxy-β-trifluoromethyl ketones,7 R-trifluoromethyl
amines, R-trifluoromethyl alcohols,8 β-trifluoromethylated
amino acids, amino alcohols, amino esters,6 heterocycles
(β-lactams, piperidines, quinolines),6,9 and aryl-R-trifluoro-
methyl amino alcohols.10 Similarly, the synthesis of a variety
of difluoromethylated analogs including nitrocarbinols and
sugar analogs10,11 has been achieved using difluoroacetalde-
hyde ethyl hemiacetal. Though much work has been done in
this field, there are only a few reports on FriedelꢀCrafts
hydroxyalkylation reactions of fluoral or fluoroketones with
arenes in the literature and in all cases the reactions stopped at
the carbinol stage.12 To the best of our knowledge, there are
only two reports in the literature on hydroxyalkylation
reaction of 2,2,2-trifluoroacetophenone with aromatics in
the presence of trifluoromethanesulfonic acid (triflic acid)
leading to 1,1,1-triaryl-2,2,2-trifluoroethanes.12d,e
1,1,1-Trichloro-2,2-bis(p-chlorophenyl)ethane (DDT)
has been used worldwide as an effective pesticide tocontrol
insect-borne diseases such as malaria. DDT has been
prepared by the acid catalyzed condensation of chloral
with chlorobenzene.13 Today, the use of DDT is banned in
many countries because of its hydrophobic nature and
persistence due to its chemical stability, leading to bioac-
cumulation and biomagnification in food chains. How-
ever, DDT isstill used in somecountries tocombat disease-
carrying insects due to its efficacy as a potent insecticide.14
Trifluoroethyl aromatics have received significant
attention in agriculture as insecticides and fungicides.15
However, there are limited studies on the synthesis of
trifluoroethyl aromatics, which include reduction of diaryl
trifluoromethyl carbinols (obtained by addition of aryl
Grignard reagent to ethyl trifluoroacetate),16a replacement
of chlorine by fluorine of 2,2,2-trichloroethyl aromatics,16b
FriedelꢀCrafts reaction of R-trifluoromethyl benzyl
alcohol (prepared by reduction of R-trifluoromethyl
acetophenone),16c and treatment of arenes in trifluoroace-
tic acid with sodium borohydride.16d All these methods
have many disadvantages such as high toxicity of reagents,
poor yields, and the involvement of multistep procedures.
During our recent studies on FriedelꢀCrafts reactions
and acid catalyzed synthetic transformations under various
superacidic conditions, we found that boron trifluoride
monohydrate (BF3ꢀH2O) is a very effective acid catalyst
for the preparation of sulfides from carbonyl compounds,17
nitration of aromatics and preparation of alkyl nitrates
using metal nitrates,18 halogenation of deactivated arenes
using N-halosuccinimide,19 the Fries rearrangement of
phenolic esters,20 and preparation of di- or triarylmethane
derivatives from heteroaromatic and aromatic carboxalde-
hydes, respectively, andanthracene derivatives from phtha-
lic dicarboxaldehyde under relatively mild conditions.21
Herein, we describe the synthesis of 1,1,1-trifluoro-2,2-
diarylethanes (3aꢀi) and 1,1-difluoro-2,2-diarylethanes
(4aꢀh) from arenes and fluorinated acetaldehyde hemiace-
tals in a single step in BF3ꢀH2O without the use of any other
organic solvents. 1,1,1-Trifluoro-2,2-diarylethane and 1,1-
difluoro-2,2-diarylethane derivatives are the fluoroanalogs
of DDT.22 BF3ꢀH2O plays a dual role, as an efficient acid
catalyst as well as a suitable medium for this reaction.
Scheme 1. Synthesis of 1,1,1-Trifluoro-2,2-diarylethanes (3aꢀi),
1,1-Difluoro-2,2-diarylethanes (4aꢀh) under BF3ꢀH2O Cata-
lyzed Conditions and Mixture of Carbinol 5a and Ether 5a0
under Less Acidic Conditions
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