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Mechanism of the Rearrangement of Flavan Derivatives on Reduction with LiAlH4AlCl3.

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[3] K. Dehnicke and U . Miiller, Angew. Chem. 76, 385 (1964);
Angew. Chem. internat. Edit. 3, 448 (1964); Z. anorg. allg.
Chem., in press.
[4] A . Schmidt, Z.anorg. allg. Chem., in press.
[5] R . Mecke and W. KutzelrziEg, Spectrochim. Acta 16, 1225
(1960).
[6] I. R . Beattie and M . Webster, J. chem. SOC.(London) 1963,38.
[7] C. V . Hart, J. Amer. chern. SOC.50, 1922 (1928).
[8] F. D. Marsh and M . E. Hermes, J. Amer. chem. SOC.86,
4506 (1964).
Mechanism of the Rearrangement of Flavan
Derivatives on Reduction with LiAIH4/AIC1,
By Dr. K. Weinges and F. Nader
Organisch-Chemisches Institut,
Universitat Heidelberg (Germany)
When a flavan containing a 4‘-methoxy and a free 3-hydroxy
group is reduced with LiAIH4/3AlC13, the 1,3-diaryl-2propanol derivative produced is accompanied by a rearrangement product, namely, the derivative of a 2.3-diarvl-lpropanol [I]. We have studied the course of the rearrangement
(I).
by means of [2-14C]-3’-,4’,7-trimethoxy-3-flavanol
When ( I ) is reduced with LiAIH4/3 AIC13 in tetrahydrofuran
and the product is methylated with diazomethane in ether,
the compounds (2) and (3) are formed in the molar ratio
2.3:l and with a total yield of 61 X.T o elucidate the position
of the 14C, the product (3) was oxidized to the acid which
was then degraded according to the Curtius reaction. The
resulting amine gave, on Hofmann elimination, the stilbene
(4), oxidation of which afforded veratric acid (5) and 0,Odimethylresorcylic acid (6). The acids were separated as
diphenylmethyl esters. Only the veratric acid (5) was radioactive, i.e. C-4 of the flavanol must migrate from C-3 to C-2.
Monomeric Boron Imides
By Dr. P. I. Paetzold and W. M. Simson
Institut fur Anorganische Chemie,
Universitat Munchen (Germany)
When dichloro(pentafluorophenyl)borane and an equivalent
amount of an aromatic amine are kept in boiling benzene for
2 days, they afford the monomeric boron imides ( I ) and (2)
in 73 and 83 % yield, respectively, m e t h e r with the calculated quantities of HCI:
CsFsBC12 + ArNH2
--f
2 HCI
+ CsFSB=NAr
OC H3
f I ) , A r = p-CH3O-CsH4( 2 ) , Arr- mesityl
C H 3 0 a 0 c H 3 f 6 0 C H 3
OCH3
c
H
3
0
eH -C
\
HZ
H
CH,Y~:OH
3
OH
(1)
= 14c
The product ( I ) is accompanied, in 13 % yield, by the dimer
(3)),~ which is a further repre(C~FSB-N-C~H~-OCH~
sentative of the series of 1,3,2,4-diazadiboretidinesf1-31, but
formation of (2) is not accompanied by that of the dimer,
presumably for steric reasons. Compounds ( I ) , (2), and
(3) were characterized by
and by cryoscopic and osmometric determinations of molecular weight
in benzene.
The Raman spectrum of ( I ) includes an intense band at
1703 cm-1 with a subsidiary band at 1710 cm-1, which we
assign to the 11BN and loBN stretching vibrations. From the
observation that the BN vibration (but not its overtone at
3400 cm-1) is IR-inactive we conclude that the BN bond in
compound ( I ) is nonpolar and that the BN vibration is
independent of the neighboring polar groups. The nonpolarity of the BN bond is assumed to be caused by the
strong electron attraction of the C6F5 group, which not
only draws negative charge from the N atom but also
strengthens the two possible BN x-bonds.
With pyridine in benzene, compound ( I ) forms a colorless,
crystalline 1:1 adduct. Treatment of compound ( I ) with a
solution of HCl in diethyl ether cleaves it to p-methoxyanilinium chloride and C6F5BC12; the latter is obtained in
only moderate yield. With dimethyl 1,2,4,5-tetrazine-3,6dicarboxylate in dioxane, compound ( I ) reacts with liberation
of nitrogen and formation of a compound of formula
C ~ ~ H I ~ O ~(colorless
N ~ F ~ crystals
B
from benzene), which
seems to be the product of a Diels-Alder-type reaction with
( I ) as a dienophile.
Received: July 13th, 1966
German version:
Chem.
[z 285 IEl
825 (1966)
[l] M . F. Lappert and M . K. Mujumdnr, Proc. chem. SOC.(London) 1963, 88.
[2] P. I. Paetzold, 2. anorg. allg. Chem. 326, 53 (1963).
[3] P. 1. Paetzold, P. P. Hubereder, and R . Miillbauer, J. organomet. Chem., in press.
842
OCH3
OCH,
(3)
OC H3
(4)
(6)
Probably the hydridodichloroaluminum AIHC12 formed from
LiA1H4/3AICI3 attacks the benzyl ether oxygen atom,
yielding the carbenium ion (8), which yields the more stable
carbenium ions (7) and (9). The ion (7) arises by migration
from C-4, the nucleophilicity of this C atom playing a large
part in controlling the yield of (3) [the molar ratio (2) :(3) is
1.2:1 if a further OCH3 group is attached to C-51. The ion
(9) arises by hydride shift; that this actually occurs is shown
HZ
Hz
I 7)
(8)
+
a1 = AlHC1,
HZ
(9)
by reduction of the flavan ( I ) with LiAID4/3AIC13; it was
proved by mass spectrometry and N M R spectrometry that
the deuterium in compound (2) is then attached to C-2 and
C-3 (flavan numbering) in the atomic ratio 3:2.
Received: July 13th, 1966
[Z 291 IE]
German version: Angew. Chem. 78, 826 (1966)
~
[l] J . W. Clark-Lewis, J. chem. SOC.(London) 1960, 2433.
Angew. Chem. internat. Edit. J Vol. 5 (1966) / No. 9
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flava, rearrangements, lialh4alcl3, mechanism, reduction, derivatives
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