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Cycloadditions of N-Methoxycarbonyl-2 3-homopyrrole.

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interconversion of the now mobile, "dynamically planar" chelate rings.
For unbridged 1,Z-enedithiolates containing no other kind of
ligand attached to the central ion approximately planar chelate
ring structures have been found in the solid state"]; however,
there are cases in which the ring is known to be folded[8]. The
above results for solutions of (1)-(3) together with the analogous chelate ring folding in crystalline (C,H5),M~S2C6H,[21
demonstrate that the planar structure (b) recently proposed[']
for metallocene enedithiolate chelates cannot be regarded as
generally valid.
1,3- and 1,4-cyclohexadiene has a half-life of 30 min at
339.4"C['] the isomerization of ( I ) proceeds to completion
within 30 min at 285°C. If a similar mechanism is assumed
for the isomerization of ( I ) as has been proposed for bicyclo[3.1.0]hex-2-ene then the greater ease with which (1)rearranges is consistent with a greater stability of the delocalized
intermediate (6) compared to the biradical (5).
COzCH3
(61
(5)
(IJ
(2)
(3)
3.94
3.92
4.10
22
+20
38
+10
+15
38
Attempts to detect the aziridine (7) that should result from the
presumably even more facile vinyl-cyclopropane rearrangement[8'10]have been unsuccessful. Carrying out the reaction at
245" C gave only a 30% conversion to the dihydropyridine (4).
No other product could be detected.
14.8
14.0
14.3
Received- November 26,1970 [Z 331 I€]
German version: Angew. Chem 83, 146 (1971)
Synthesis and Themolysis
of N-Met hoxycarbonyl-2,3-hornopyrr~le[~~
It is possible that aziridine (7) is thermally less stable than cyclopropane ( I ) and its equilibrium concentration is too small
to detect. We believe this is unlikely and doubt that (7) is ever
being formed. This conclusion is based on the known facd9]
that heating (8) gives the oxazoline (9) and neither the corresponding homopyrrole nor dihydropyridine. Orbital symmetry
considerations also suggest that the interconversion of (6) with
( I ) should be more favorable than (6) with (7) which is consistent with our observations["].
By Frank W . Fowler"]
We report that the cuprous chloride catalyzed decomposition
of diazomethane in the presence of N-methoxycarbonylpyrrole
produces mainly N-methoxycarbonyl-2,3-homopyrrole( N methoxycarbonyl-2-azabicyclo[3.l.O]hex-3-ene) (1) in addition to smaller amounts of the bishomopyrroles (2) and (3)
(3 : 1:0.6).
R
R
R
( 71
(8)
(9)
Received. November 23, 1970 [Z 317a IE]
German version: Angew. Chem. 83, 147 (1971)
R
[*] Prof. Dr. F. W. Fowler
Chemistry Department, State University of New York
Stony Brook, New York 11790 (USA)
TheNMR spectrum(CDCI3)of (1)showsr = 3.60(1H/broad,s),
4.53-4.70 (lHim), 5.83-6.28 (lH/m), 6.22 (3H/s), 7.75-8.00
(lH/m), 8.98-9.37 (lH/m), and 9.83-10.08 (lH/m). This
spectrum remains essentially unchanged from room temperature to 170°C except that the vinylic hydrogen adjacent to
the nitrogen atom appears as a doublet at high temperature
and a broad singlet at room temperature. This observation is
attributed to hindered rotation of the methoxycarbonyl group
at room temperature.
Previous studies have shown that the copper catalyzed
decomposition of diazo compounds in the presence of pyrrole
and its N-methyl derivative yields only substitution products[3]
The formation of addition rather than substitution products with
N-methoxycarbonylpyrroleis attributable to the known ability
of the N-methoxycarbonyl group to cause pyrrole to behave
as a dienei4].
Pyrolysis of (1) in the gas phase at 285" C produced a nearly
quantitative yield of N-methoxycarbonyl- 1Jdihydropyridine
(4). The NMR spectrum (CDCI,) is similar to that previously
reported for N-phenyl- 1,2-dihydr0pyridine[~]. Reduction of
(4) (LiAIH,) gives the known N-methyl derivative[6].
[ I ] We are indebted to the National Science Foundation for partial support of this work.
[2] Presented at the IUPAC Conference on Cycloaddition Reactions
at Miinchen, September, 1970.
131 C. W. Rees and C. E. Smithen, Advan. Heterocyclic Chem. 3, 57
(1964).
[4] For example, N-methoxycarbonylpyrroleis one of the few pyrroles
that undergoes the Diels-Alder reaction; R. M. Acheson and 1.M. Vernon, J . Chem. SOC.1961, 457.
[S] M. Saunders and E. H. Gold, J. Org. Chem. 27, 1439 (1962).
[6] E. M. Fry, J. Org. Chem. 29, 1647 (1964).
[7] R . J. Ellisand H. M. Frey, J. Chem. SOC.A 1966, 553.
[S] W. v. E. Doering and W. R. Roth, Angew. Chem. 75, 27 (1963);
Angew. Chem. internat Edit. 2, 115 (1963).
[9] A. Mishra, S. N. Rice, and W. Lwowski, J. Org. Chem. 33, 481
(1968).
[lo] For a discussion as to whether a diradical is involved in vinyl-cyclopropane rearrangements see M. R. Willcott, III and V. H. Cargle,
J. Amer. Chem. SOC.91,4130 (1969).
[ 111 R. B. Woodward and R. Hoffmann, Angew. Chem. 81,797 (1969);
Angew. Chem. internat. Edit. 8, 781 (1969).
Cycloadditions
of N-Methoxycarbonyl-2,3-homopyrrole~1~z~
By Frank W. Fowler[*]
A comparison of the thermal isomerization of ( I ) with the carbocyclic analog indicates that the heterocycle rearranges more
readily. Whereas the thermolysis of bicyclo[3.1 .O]hex-2-ene to
Angew. Chem. internat.
Edit./ Vol. 10 (1971) / N o . 2
N-Methoxycarbonyl-2,3-homopyrrole
(N-methoxycarbonyl-2azabicyclo[3.1 .O]hex-3-ene) (1
reacts with dimethyl
acetylenedicarboxylate to give the cycloadduct (Z)141 [NMR
135
spectrum (CDCl3): 7 = 3.50 - 3.83 (H2/m), 4.25 - 4.61
(H3/m),4.90(H6/d,J= 5.5Hz),5.11(H1/d,J=5.0Hz),6.18
(6 methyl-His), 6.27 (3 methyl-His), and 7.55 (H4, H5/center
of broad AB)].
nearly zero coupling to the adjacent hydrogen Hb It follows
from the above discussion that H b must occupy the endo position.
C OzC H3
COZCH,
0'
70 2 C H3
@
o - - H
+ CH302C-Cn-C-C02CH~
The above assignments were deduced from double resonance
experiments. It is interesting to observe that H6 occurs as a
doublet suggesting zero coupling between H6 and either H4 or
H5. Dreiding molecular models and a comparison with the carbocyclic system['] indicate that the bond to H6 forms an angle
of approximately 90" with the adjacent bond to the endo
hydrogen. This would suggest that zero coupling occurs between
H6 and the endo hydrogen H'.
N-Phenylmaleimide also reacts with (1a) to give two isomeric
adducts in the ratio 2 : 3 which could be separated by preparative
layer chromatography. The product (3) is assigned the ex0 configuration since the bridgehead hydrogens H and H' appear as
an AB pattern shywing zero coupling to the bridgehead hydrogens Ha, and H a . Hydrogenation of (3) gives a symmetrical
structure where the hydrogens that were responsible for the
AB pattern now appear as a singlet. This result is consistent
with the above assignment.
O R
I
0 ON,
U , - H
R
(a), R
(b), R
= H
= COzCzH5
These results can be explained in terms of dipole (5) which can
be formed by a thermally allowed disrotatory ring opening of
(1). (Sb) can undergo a 2+4 cycloaddition from the sterically
unhindered side to give the observed product (Zb).
A concerted mechanism requires that the dienophile approach
the homopyrrole from the endo direction. Molecular models
indicate that electronically this type of attack is most favorable.
That is, the cyclopropane bond that is being broken can be more
nearly colinear with the p-orbital of the dienophile when attack
occurs from the endo direction['].
Received November 23, 1970 [Z 317 bl
German version: Angew. Chem. 83, 148 (1971)
[*I
Prof. Dr. F. W. Fowler
Chemistry Department, State University of New York
Stony Brook, New York 11790 (USA)
[ 11 We are indebted to the National Science Foundation for partial support of this work.
[Z] Presented by F. W. Fowler to the IWAC Conference on Cycloaddition Reactions at Miinchen, September, 1970.
[3] F. W. Fowler, Angew. Chem. 83, 147 (1971);Angew. Chem. internat. Edit. lo, 135 (1971).
[4] This is formally a Diels-Alder reaction involving a homodiene. Previously, there has been reported only one example of this type of transformation; S. SarelandE. Brener, J. Amer. Chem. SOC.81,6522 (1959).
IS] C. W. Jefford, B. Waegell, and K. Ramez, J. Amer. Chem. SOC.87,
2191 (1965).
[ 6 ] F. W. Fowler, Chem. Commun. 1969, 1359.
[7] The radical reactions of bicyclo[l.l.O]butane and hicyclo[2.1.0]pentane with olefins also occurs from the endodirection. Electronically,
these reactions are analogous and consistent with a concerted mechanism; P. G. Gassman, K. T. Mansfield, and T. J. Muphy, J . Amer.
Chem. SOC.91, 1685 (1969); M Pomerantz, G. W. Gruber, and R. N.
Wilke, ibid., 90, 5040 (1968).
Hydrogendicarboxylate Ions as
Hydrogen Bonded Chelate Systems
in Organoantimony Compounddl1
The reaction of the homopyrrole with N-phenylmaleimide is
first order with respect to both the homopyrrole and dienophile
and shows almost n o solvent dependence (kCCL=1.36 +-0.11x
1 mole-'s-'
and kcH,C--N = 1.17 f 0.30 x
1 mole-'s-' at 75.08"C).
(2b)
The reaction of DMAD with homopyrrole (lb)I6] follows an
interesting course. There are two possible stereoisomers obtainable from this reaction. Only isomer (2b)is formed which readily
rearranges on silica gel to the conjugated isomer. The stereochemical assignment of (26) is based o n the NMR spectrum.
The bridge hydrogen Ha appears as a broad singlet indicating
136
By Hubert Schmidbaur and Karl-Heinz Mitschke ['I
It was observed during systematic studies on the coordination
chemistry of antimony in compounds of type R,SbX[21 that the
acceptor strength of the central atom is reduced considerably
by the inductive effect of four organic groups R. Many of these
compounds are consequently found to exist as monomeric, covalently bonded molecules; only in some cases are weak intermolecular interactions detectable and then only in the solid state
(X = F, OH). Adducts of the type R4SbXL in which Lrepresents
a monofunctional donor are IargeIy unknown13]. However, we
have now found that a R4SbXL adduct can exist when X and
L are additionally linked by a hydrogen bond. We wish to report
on the first representatives of this type of compound in the present communication.
The tetramethylantimony carboxylates (l)L41,which may be obtained from equimolar amounts of pentamethylantimony and
a carboxylicacid R'COOH with elimination of methane, are volatile monomeric compounds containing pentacoordinated antimony: they are readily soluble in nonpolar solvents. Addition
of a further mole of carboxylic acid leads to stable 1 : 1 adducts
(2) which crystallize readily and whose acid content can easily
be determined by titration.Elementa1 analysis provides confirmatory evidence for their composition. According to cryoscopic
and ebullioscopic molecular weight determinations in benzene
Angew. Chem. internat. Edit. / VoI. 10 (1971) / N o . 2
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