Mediated hydrolysis of benzonitrile initiated by NaBH4

Full text of DOI:10.1007/s10593-008-0022-8

Chemistry of Heterocyclic Compounds, Vol. 44, No. 2, 2008
LETTERS TO THE EDITOR
MEDIATED HYDROLYSIS OF BENZO-
NITRILE INITIATED BY NaBH4
M. I. Khasanov and S. S. Mochalov
Keywords: 5,6-ethylenedioxy-3-phenylphthalide, 2-cyano-4,5-ethylenedioxybenzophenones, mediated
hydrolysis.
Benzonitriles do not react with NaBH4, though they can be reduced by the action of diborane to give
benzylamines. The discrepancy in the reductive activity of these boron hydrides has been attributed to the
capacity of diborane, in contrast to NaBH4, to coordinate at the cyano group nitrogen atom, thereby enhancing
the activity of the cyano group carbon atom toward nucleophilic attack of the hydrogen atom in the B-H bond
[1].
In our search for a synthesis of ortho-cyanobenzhydrols such as 2 required for a study of intramolecular
acid-catalyzed cyclization and considering the inertness of the cyano group under NaBH4 reduction conditions,
we attempted to reduce the carbonyl group in 2-cyano-4,5-ethylenedioxybenzophenone to a alcoholic group by
the action of this reducing agent. However, we found that in conditions, under which, for example,
ethylenedioxybenzophenones containing amide fragments in the ortho position readily form the corresponding
benzhydrols [2], cyanobenzophenone 1 is converted to 3-phenylphthalide 3 in high yield rather than alcohol 2.
OH
O
Ph
Ph
O
CN
Ph
O
O
O
NaBH4
2
CN
O
O
B
1
–
H
O
H
NH
Ph
O
A
O
HCl
H2O
O
O
3
__________________________________________________________________________________________
M. V. Lomonosov Moscow State University, 119992 Moscow, Russia; e-mail: ssmoch@org.chemmsu.ru.
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 293-294, February, 2008. Original article
submitted January 16, 2008.
0009-3122/08/4402-0225©2008 Springer Science+Business Media, Inc.
225

This result may be interpreted as a sequence of reduction reactions of the carbonyl group, mediated
hydrolysis of the cyano group, and intramolecular cyclization. We propose that intermediate A, probably already
formed under reducing conditions, is responsible for the mediated hydrolysis of the cyano group.
1
The H NMR spectrum was taken on a Varian VXR-400 spectrometer at 400 MHz in CDCl3 with
residual CDCl3 as the internal standard. The electron impact mass spectrum was taken on a Finnigan MAT
INCOS 50 mass spectrometer at 70 eV.
5,6-Ethylenedioxy-3-phenylphthalide (3). 2-Cyano-4,5-ethylenedioxybenzophenone (1) (2.61 g, 0.01
mol) was added with stirring to a suspension of NaBH4 (0.38 g, 0.01 mol) in ethanol (32 ml) over 30 min. The
reaction mixture was heated at 40-50°C and then left for 24 h and then 10% hydrochloric acid was added
dropwise until the mixture was slightly acidic. The reaction mixture was poured into water (150 ml) and heated
at reflux for 1 h. The precipitate formed was filtered off and recrystallized from ethanol to give 2.35 g (88%) 3,
mp 167-168°C. 1H NMR spectrum, δ, ppm (J, Hz): 4.26-4.31 (4H, m, OCH2CH2O); 6.26 (1H, s, CHC6H5); 6.75
(1H, s, H-4); 7.24-7.28 (2H, m) and 7.35-7.38 (3H, m, ArH); 7.40 (1H, s, H-7). Electron impact mass spectrum,
ν, cm-1: 268 [M]+ (78), 239 (23), 191 (26), 168 (32), 163 (100), 152 (10), 139 (90), 134 (31), 127 (12), 105 (32),
89 (12), 77 (84), 74 (24), 69 (18), 63 (36), 50 (90), 39 (19). Found, %: C 71.41; H 4.32. C16H12O4. Calculated,
%: C 71.63; H 4.51.
REFERENCES
1.
2.
G. Tennant, in: Comprehensive Organic Chemistry [Russian translation], vol. 3, Khimiya, Moscow
(1982), p. 675.
R. A. Gazzaeva, M. I. Khasanov, S. S. Mochalov, and N. S. Zefirov, Khim. Geterotsikl. Soedin., 941
(2007). [Chem. Heterocycl. Comp., 43, 799 (2007)].
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