Reaction of stereoisomeric 2,4,5-substituted 1,3,2-dioxaborinanes with paraformaldehyde

Full text of DOI:10.1023/A:1013172730470

Russian Journal of Organic Chemistry, Vol. 37, No. 9, 2001, pp. 1359 1360. Translated from Zhurnal Organicheskoi Khimii, Vol. 37, No. 9, 2001,
pp. 1423 1424.
Original Russian Text Copyright
2001 by Kuznetsov.
SHORT
COMMUNICATIONS
Reaction of Stereoisomeric 2,4,5-Substituted
1,3,2-Dioxaborinanes with Paraformaldehyde
V. V. Kuznetsov
Ufa State Petroleum Technical University, ul. Kosmonavtov 1, Ufa, 450062 Bashkortostan, Russia
e-mail: physics@oil.rb.ru
Bogatskii Physicochemical Institute, Ukrainian National Academy of Sciences,
Lyustdorfskaya doroga 86, Odessa, 270080 Ukraine
Received September 15, 2000
Reactions of six-membered cyclic boronic acid
esters with aldehydes are known to result in formation
of the corresponding 1,3-dioxanes [1, 2]. The present
communication reports on the stereochemical features
of reactions of a series of 2,4,5-substituted 1,3,2-di-
oxaborinanes I III with paraformaldehyde. According
to the GLC data, these reactions lead to formation
of 4,5-disubstituted 1,3-dioxanes IV VI:
equilibrium mixture is greater than the expected value.
Taking into account the accuracy of the GLC deter-
mination ( 3% [4]), the reaction of trans-esters I and
II with paraformaldehyde is somewhat faster than
the reaction of their cis isomers. As a result, increased
fraction of trans-IV and trans-V is observed in the
equilibrium mixture. Such a difference in the reaction
rates is typical of configurationally stable 1,3,2-dioxa-
borinanes I and II. By special experiments we showed
that no isomerization of I and II occurs by the action
of ZnCl2 in the reaction with paraformaldehyde. Ob-
viously, the reason lies in the specificity of the reac-
tion mechanism which involves initial coordination of
the carbonyl oxygen atom to boron or of the carbonyl
carbon atom to the ring oxygen atom with subsequent
rupture of the B O bond and formation of new C O
bond [5]. However, the ability of boronic ester III to
I, IV, R = i-Pr, R = Me; II, V, R = PhCH2, R = Me;
III, VI, R = Me, R = Ph.
Stereoisomeric composition of cyclic boronic acid esters
I and II and products of their reaction with paraformalde-
hyde (1,3-dioxanes IV and V)
Two samples of compound I with cis trans isomer
ratios of 77:33 and 35:65 were used. The reaction
occurs only in the presence of a catalytic amount of
anhydrous ZnCl2. Dioxanes IV VI were identified
by comparing with authentic samples which were
prepared as described in [3]. The highest conversion
of ester I was 25%, of II, 20%, and of III, no greater
than 1% (according to the GLC data). The stereo-
isomeric compositions of the initial and equilibrium
mixtures are given in table (for 1,3-dioxanes, given
is the isomer ratio of samples prepared by independent
method from the corresponding 1,3-diols and para-
formaldehyde). It is seen that equilibrium mixtures
are characterized by increased fraction of the cis
isomers, as compared to the initial isomer ratio. By
contrast, the fraction of trans-1,3-dioxanes in the
cis trans Isomer ratio
Compound
no.
initiala
equilibrium
I
IV
I
IV
II
V
77: 23
67: 33
35: 65
39: 61
66: 34
66: 34
88: 12
62: 38
48: 52
33: 67
68: 32
57: 43
a
Given is the isomer ratio of samples of IV and V prepared by
independent method.
1070-4280/01/3709-1359$25.00 2001 MAIK Nauka/Interperiodica

1360
KUZNETSOV
undergo isomerization with cleavage of the C O
bond in the presence of ZnCl2 [6], considerably
reduces its reactivity toward paraformaldehyde.
ZnCl2 was placed in an ampule and was heated for
8 h at 130 C; samples were withdrawn intermittently
and were analyzed by GLC.
1
The H NMR spectra were obtained on a Bruker
AM-300 instrument from 10% solutions in CDCl3
containing TMS as reference. GLC analysis was
performed on a Tsvet-126 chromatograph equipped
with a flame-ionization detector; 3000 4-mm column
packed with 5% of OV-17 on Chromaton N-Super;
carrier gas argon. The components were quantitated
by the internal normalization technique using calibra-
tion coefficients determined according to [4].
Our results indicate some influence of the substit-
uent and configuration on the reactivity of cyclic
boronic esters in processes involving cleavage of the
B O bond. On the other hand, in contrast to earlier
data [7], the reaction of 1,3,2-dioxaborinanes with
aldehydes is stereospecific, for it does not involve
rupture of bonds at chiral centers.
REFERENCES
1. Kuznetsov, V.V. and Gren’, A.I., Zh. Obshch. Khim.,
1983, vol. 53, no. 6, pp. 1432 1433.
2. Gren’, A.I. and Kuznetsov, V.V., Khimiya tsikliches-
kikh efirov bornykh kislot (Chemistry of Cyclic Boron
Acid Esters), Kiev: Naukova Dumka, 1988.
Compounds I III were synthesized as described
in [2, 6]. A sample of I containing 77% of the cis
isomer and 23% of the trans isomer was prepared
from 2-isopropyl-1,3-butanediol which was in turn
synthesized by reduction of ethyl isopropylaceto-
acetate with lithium aluminum hydride according to
the procedure reported in [8]; a sample of I with
a cis trans-isomer ratio of 35:65 was obtained from
the same diol with increased fraction of the threo-
isomer; it was synthesized in 45% yield by reduction
of 0.1 mol of ethyl isopropylacetoacetate with NaAlH4
(equimolar amount) in THF in the presence of 0.2 mol
of dibenzo-18-crown-6 [9]. The configurational
stabilities and stereoisomeric compositions of com-
pounds II and III were determined in [6]; the isomer
ratios of samples of ester I were determined in this
3. Rakhmankulov, D.L., Syrkin, A.M., Karakha-
nov, R.A., Kantor, E.A., Zlotskii, S.S., and Ima-
shev, U.B., Fiziko-khimicheskie svoistva 1,3-dioksanov
(Physicochemical Properties of 1,3-Dioxanes),
Moscow: Khimiya, 1980.
4. Vyakhirev, D.A. and Shushunova, A.F., Rukovodstvo
po gazovoi khromatografii (A Guide to Gas Chrom-
atography), Moscow: Vysshaya Shkola, 1975, p. 129.
5. Kalyuskii, A.R., Zhuchenko, S.E., Kuznetsov, V.V.,
and Gren’, A.I., Zh. Org. Khim., 1989, vol. 25, no. 10,
pp. 2202 2204.
6. Kuznetsov, V.V., Alekseeva, E.A., and Gren’, A.I.,
Khim. Geterotsikl. Soedin., 1995, no. 9, pp. 1291
1294.
1
work. H NMR spectrum, , ppm (J, Hz): cis-Ia:
3.69 m (1H, 6-HA), 3.94 m (1H, 6-HB), 4.17 m
(1H, 4-H), 1.11 d (3H, 4-CH3), 1.31 m (1H, 5-H,
7. Kuznetsov, V.V. and Gren’, A.I., Zh. Org. Khim.,
1985, vol. 21, no. 9, pp. 2016 2017.
3
3JAX = 11.5, JBX = 5.0); trans-I: 3.75 m (1H, 6-HA),
8. Bogatskij, A.V., Samitov, Ju.Ju., Gren, A.I., and
Soboleva, S.G., Tetrahedron, 1975, vol. 31, no. 6,
pp. 489 494.
3.92 m (1H, 6-HB), 3.97 m (1H, 4-H), 1.21 d (3H,
4-CH3), 1.31 m (1H, 5-H, 3JAX = 8.6, 3JBX = 4.1).
Reaction of 1,3,2-dioxaborinanes I III with
paraformaldehyde. A mixture of 0.01 mol of ester
I III, 0.05 mol of paraformaldehyde, and 0.5 g of
9. Bogatskii, A.V., Luk’yanenko, N.G., Lyamtseva, L.N.,
Teterina, T.G., and Vasilova, I., Zh. Org. Khim., 1981,
vol. 17, no. 6, pp. 1202 1204.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 9 2001