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Optically Active 2-Methylazaferrocene.

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alkenes, either disubstituted or trisubstituted. It is of interest
that such unreactive alkenes do not undergo hydroxymercuration either.
The observed order of reactivity closely parallels the known
order of alkeiie-silver(i) stability constants 141, and suggests
a mechanism (eq. 1) involving a rapid prior equilibrium,
giving an ion ( I ) , which reacts with azide ion in a slow step
to yield ( 2 ) . The remarkable efficiency with which azide
competes with water in the reaction argues strongly for the
existence of the ionic intermediate ( I ) , since kN,-/kH,O is
known to increase greatly with increasing delocalization of a
cation J 5 J .
Cotton effects are shifted only slightly: ( I ) in ether, -0.15
(515 nm) and +0.15 (445 nm); ( I ) in 0.1 N HCI, -0.19
(496 nm) and +0.20 (421 nm); ( I ) . BF3 in ether, -0.31
(500 nm) and +0.32 (435 nm) (cf. Fig. 1).
3c
I*’\
A
is
Received: Noveniber 28, 1968
[Z 909 IEI
tierman version: Angew. Chem. 81, 148 (1969)
[‘I Prof. Dr. C. H. Heathcock
Department of Chemistry
University of California
Berkeley, California 94720 (USA)
[**I Financial support of this work by the National Science
Foundation and the Alfred P. Sloan Foundation is gratefully
acknowledged.
[l] a) J . Chatt, Chem. Ber. 48, 7 (1951); b) N . S. Zefirov, Russ.
Chem. Rev. (English translation of Usp. Chim) 34, 527 (1965).
[2] H . C. Brown and P . Ceohagen, J. Amer. chem. SOC.,89, 1522
(1967).
[3] Caution: Solid mercuric azide is sensitive to light and shock.
The salt is insoluble in water, but readily dissolves in 50oL,aqueous
tetrahydrofuran. We have found that such solutions may be
handled without danger.
[4] S. Winstein and H . J . Lucas, J . Amer. chem. SOC.60, 836
(1938).
151 R. A . Sneen, J . V. Carter, and P. S. Kay, J. Amer. chem. SOC.
88, 2594 (1966).
Optically Active 2-MethylazaferroceneI* *I
By K . Bauer, H . Falk, and K . Schlogl[*1
Unsymmetrically disubstituted metallocenes belong to the
point group C1; they are therefore chiral and can be obtained
in optically active forms [IJ. This symmetry condition is also
valid for homoannularlymonosubstituted azaferrocenes, which
therefore should be resolvable into optical antipodes. This
could now be verified for 2-methylazaferrocene ( I ) .
12
300
590
LOO
Xhlnrnl
600
--z
Fig. 1. ORD and C D curves and U V spectrum of ( I ) in cyclohexane,
CD curve of ( I ) . BF, in ether.
The ORD curve of ( I ) is very similar to that of a-ethynyl- and
cr-cyanomethylferrocene, compounds (2) and ( 3 )151, respectively, in which no conformational contributions (of substituents) t o the optical activity are possible either (cf. “1).
This analogy, together with the fact that salt formation
@rotonation o r addition of BF3) increases the activity of the
“metallocene absorption band” in the region of 430 nm, may
be considered as evidence that the ring nitrogen dominates
over the methyl group with regard to the perturbance of the
metallocene chromophore 161, as does C = C H or C 3 N in (2)
and (31, respectively.
Therefore, the assumptions seems to be justified that (-)-(Z),
(-)-(2), and (-)-(3) with positive Cotton effects around
430 n m have identical chiralities, and that ( - ) - ( I ) conseand (+)-methylquently [by analogy with (-)-(2), (-)-(.3),
ferrocene-r-carboxylic acid] [ 5 ] has the absolute configuration ( 2 R ) “1.
Received: December 9, 1968
[Z 910 IEI
German version: Angew. Chern. 81, 150 (1969)
[*I Prof. K. Schlogl, Dr. H. Falk, and K. Bauer
Organisch-Chemisches Institut der Universitiit
A-1090 Wien, Wahringerstrasse 38 (Austria)
Racemic ( I ) was obtained in 45% yield as a n oil from the
potassium salt of 2-methylpyrrole and C ~ H ~ F ~ ( C Oin
) ZdiI
oxane 121. Elemental analysis, N M R spectrum [CDCI3,
methyl protons a t 6 = 2.32, ring protons at 5.34 (IH), 4.50
(2H), and 4.22 (5H)], and mass spectrum[31 [nzie - 201
(CloH11FeN)+, 186 (M-CH3)I,
135 (C5H5FeN)+, 121
(C5H5Fe)+, and 80 (CsHsN)+] prove the structure ( I ) .
Reaction of ( 1 ) with a n equimolar amount of (-)-6,6‘-dinitrodiphenic acid in ethanol afforded a n amorphous precipitate; addition of petroleum ether to the mother liquor yielded
a crystalline, rather unstable salt, which was recrystallized
twice from acetone. This salt afforded levorotatory ( I ) :
[al2,” = -62’ (c = 0.04, cyclohexane)[4J, m.p. 42-52’C.
( + ) - ( I ) , [a]: = +33O, was obtained from the mother liquor
of the salt crystallization.
T h e O R D and C D curves, and the U V spectrum of ( - ) - ( I )
are reproduced in Fig. 1. i n 0.1 N hydrochloric acid or on
addition of B F ~ - O ( C Z H the
~ ) ~ &-values are increased,
whereas the sign of rotation remains unchanged and the
Angew. Chem. internat. Edit. 1 Vol.8 (1969)
/ No. 2
[**I This work was supported by the “Osterr. Fonds zur Forderung der wissenschaftlichen Forschung”.
[l] K. Schlogl, Fortschr. chem. Forsch. 6, 479 (1966); Topics in
Stereochemistry, Interscience, New York 1967. Vol. I , p, 39.
[2] For the synthesis of azaferrocene and its methyl derivatives
in benzene cf.: K . K . Joshi, P. L. Pauson, A . R . Qazi, and W. H .
Stubbs, J. organometallic Chem. I , 471 (1964). If dioxane is
employed, the yield of azaferrocene can be increased from 22 to
36Y,.
I31 We are indebted to Dr. G. Schaden, Darmstadt, for recording,
and Dr. H . Egger, Wien, for the interpretation of the mass
spectrum. For the mass spectrum of azaferrocene cf.: F. See/ and
V . Sperber, J. organometallic Chem. 14,405 (1968).
[4] The optical purity of ( I ) is unknown. A tentative estimate
(30-40ob) seems feasible on comparing the A&-values(around
430 nm, “metaflocene absorption band”) of ( I ) with those of
compounds such as (21, ( 3 ) , or methylferrocene-a-carboxylic
acid, which are similar with regard to the origin of their optical
activity.
[ 5 ] G. Haller and K. Schlogl, Mh. Chem. 98, 603 (1967).
[6] The &-values of ( I ) and its salts are almost directly proportional to the molecular refractivities of Narom., N H *, and N
BF3; the dipole moment of azaferrocene in cyclohexane is 2.06
0.05 D.
~
135
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