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New Boron Heterocycles.

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New Boron Heterocycles
By W . Kliegel[*l
In the reaction of secondary amines ( I ) with formaldehyde
the hypothetical [*I second reaction intermediate, the betaine-like formaldehyde adduct (3) of hydroxymethylamine
(2). can be trapped by esterification with hydroxydiphenylborane (4). The free electrons of the negatively charged
oxygen atom can go into the empty orbital of the boron atom,
thus leading t o fixation of the aldehyde molecule in
the ring.
Ethanolic solutions of ( I ) are heated briefly to boiling with
two molecular equivalents of formaldehyde in aqueous
solution and one molecular equivalent of ( 4 ) [21. The difficultly solubler31 compound ( 5 ) crystallizes out of the reaction solution in analytically pure form.
In the same way, N-(2-hydroxyalky1)dialkylamines ( 6 ) react
with formaldehyde and ( 4 ) to give heterocyclic compounds
having seven-membered rings ( 8 ) .
If the reaction is carried out with epoxides in place of formaldehyde, corresponding eight-membered rings (10) are
formed.
[21 Hydroxydiphenylborane was used in the form of: a) hydrate;
see H . J. Roth and H . N . El Din,Arch. Pharmaz. 295,679 (1962);
b) oxybis(dipheny1borane); see R . Neu, Chem. Ber. 87, 802
(1954); c) aminoethoxydiphenylborane: smooth transesterification; cf.M. Umland, Angew. Chem. 79,583 (1967); Angew. Chem.
internat. Edit. 6, 574 (1967); d) triphenylborane; diphenylation by
the action of amino alcohols or chelating agents; see, e.g., H. J .
Roth, R. Brandes, and Ch. Schwenke, Arch. Pharmaz. 297, 766
(1964); R. Koster and G. W. Rorermund, Liebigs Ann. Chem. 689,
40 (1965).
[3] Soluble only in strongly polar solvents such as acetic acid and
trifiuoroacetic acid, also moderately soIuble in warm pyridine or
acetonitrile.
[4] B. Sko wronska-Serafinowa, B. Ustupska-Stefaniak, and M.
Mukosza, Roczniki Chem. (Ann. SOC.chim. Polonorum) 35, 723
(1961); Chem. Abstr. 55, 23396 (1961).
151 Gaseous pyrolysis products trapped in water; formaldehyde
test with chromotropic acid, after F. Feigl: Spot Tests in Organic
Analysis. Elsevier, Amsterdam 1960, p. 350.
161 1H-NMR spectrum of (5a) in CF3COOH/CDC13/TMS:
themethylene protons of the acetal-like grouping
e
-O-CH2-NR2-CH2-Ogive a four-proton singlet at 6 = 5.13
ppm; - of (8u) in the same solvent mixture: two-proton singlet
8
for the methylene protons of the group -0-CHz-NRz5.15 ppm.
I
at 6 =
R'
P2-Hc~cH2
()
'
THCHO
Decomp.
point ("C)
I
Decomp.
point (T)
~
So)
56)
SC)
Sd)
5e)
5f)
Ra = -(CH2)34CHz.k
R2 = -(CH2)5Rz = -(CH&-O-(CHzk
R =CzHs
R =n-C&
R2 =
157
135
125
96
114
100
8a) R = C2H5, R1= H
86) R2 = -(CHd-, R1= H
R1= CH,
8 ~ )Rz = -(CHz)s-.
IOa) R = CZH5.R1= H,
R2 = CH3
106) R = CzHs, R1= R2 = H
154
106 [a]
164
203 [a]
229
[a] Present as the hydrate.
Compounds (8) and (9) are also obtained when corresponding esters of ( 4 ) and amino alcohols (11) [41 are allowed to react with formaldehyde or epoxides, as was established with
(8a) and (IOa) - identical products were obtained by both
routes. The yields vary between 30 and 70%. The colorless,
highly stable compounds decompose on heating. Formaldehyde is liberated on pyrolysis of ( 5 ) and ( 8 ) [51.
The insolubility of the heterocycles in weakly polar solvents,
their IR and NMR spectracsl, as well as their elemental
analyses, are in accord with the betaine structure suggested.
Received: April 10, 1968
[Z 798 IE]
German version: Angew. Chern. 80, 614 (1968)
[*I Dr. W. Kliegel
Institut fur Pharmazeutische Chemie
der Technischen Universitat
33 Braunschweig, Beethovenstr. 55 (Germany)
[I] P. A. S. Smith: Open-Chain Organic Nitrogen Compounds.
W. A. Benjamin, New York 1965, Vol. 1. p. 27.
626
Identification of the n-o* Transition in the
Electron Excitation Spectrum of 2-Butanone
By H.-H. Perkampus[*]
Three electronic transitions are to be considered for the
carbonyl group [I]. The spectroscopic properties of one of
these, the longwave n-n* transition, have been known for a
long time [*I. In contrast, there is still some uncertainty surrounding the electronic transition in the range 50000-56000
cm-1. In many monographs and books, this transition in the
near vacuum-ultraviolet is assigned to a n N-V transition, i.e.
to a x-x* transition analogous to that of an ethylenic doubIe
bond [31. However, according to McMurry [41 it is a permitted
n-o* transition, whose oscillator strength should be about
0.02. The x-x* transition then lies at higher wave numbers
(;j > 60000 cm-1) "1, as is evident from measurements in the
vacuum ultraviolet [51.
Angew. Chem. internat. Edit. 1 Vol. 7 (1968) 1 No. 8
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