Reactions of di(tert-butyl)diazomethane with acceptor-substituted ethylenes

Article abstract of DOI:10.1002/hlca.200790102

Di(tert-butyl)diazomethane (4) is a nucleophilic 1,3-dipole with strong steric hindrance at one terminus. In its reaction with 2,3-bis(trifluoromethyl) fumaronitrile ((E)-BTE), a highly electrophilic tetra-acceptor-substituted ethene, an imino-substituted cyclopentene 9 is formed as a 1:2 product. The open-chain zwitterion 10, assumed as intermediate, adds the second molecule of (E)-BTE. The ¹⁹F- and ¹³C-NMR spectra allow the structural assignment of two diastereoisomers, 9A and 9B. The zwitterion 10 can also be intercepted by dimethyl 2,3-dicyanofumarate (11) and furnishes diastereoisomeric cyclopentenes 12A and 12B; an X-ray-analysis of 12B confirms the 'mixed' 1:1:1 product. Competing is an (E)-BTE-catalyzed decomposition of 4 to give 2,3,4,4-tetramethylpent-1-ene (7) + N₂; the reaction of (E)-BTE with a trace of water appears to be responsible for the chain initiation. The H ₂SO₄-catalyzed decomposition of diazoalkane 4, indeed, produced the alkene 7 in high yield. The attack on the hindered diazoalkane 4 by 11 is slower than that by (E)-BTE; the zwitterionic intermediate 21 undergoes cyclization and furnishes the tetrasubstituted furan 22. In fumaronitrile, electrophilicity and steric demand are diminished, and a 1,3-cycloaddition produces the 4,5-dihydro-1H-pyrazole derivative 25. The reaction of 4 with dimethyl acetylenedicarboxylate leads to pyrazole 29 + isobutene.

Full text of DOI:10.1002/hlca.200790102

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Reactions of Di(tert-butyl)diazomethane with Acceptor-Substituted
Ethylenes1)
by Rolf Huisgen*, Peter Pçchlauer2), Grzegorz Mloston´ 3), and Kurt Polborn
Departement Chemie und Biochemie der Ludwig-Maximilians-Universität, Butenandtstrasse 5 – 13,
D-81377 München
Dedicated to Herbert Mayr on the occasion of his 60th birthday
Di(tert-butyl)diazomethane (4) is a nucleophilic 1,3-dipole with strong steric hindrance at one
terminus. In its reaction with 2,3-bis(trifluoromethyl)fumaronitrile ((E)-BTE), a highly electrophilic
tetra-acceptor-substituted ethene, an imino-substituted cyclopentene 9 is formed as a 1:2 product. The
open-chain zwitterion 10, assumed as intermediate, adds the second molecule of (E)-BTE. The 19F- and
13C-NMR spectra allow the structural assignment of two diastereoisomers, 9A and 9B. The zwitterion 10
can also be intercepted by dimethyl 2,3-dicyanofumarate (11) and furnishes diastereoisomeric
cyclopentenes 12A and 12B; an X-ray-analysis of 12B confirms the ꢀmixedꢁ 1:1:1 product. Competing
is an (E)-BTE-catalyzed decomposition of 4 to give 2,3,4,4-tetramethylpent-1-ene (7) þ N2; the reaction
of (E)-BTE with a trace of water appears to be responsible for the chain initiation. The H2SO4-catalyzed
decomposition of diazoalkane 4, indeed, produced the alkene 7 in high yield. The attack on the hindered
diazoalkane 4 by 11 is slower than that by (E)-BTE; the zwitterionic intermediate 21 undergoes
cyclization and furnishes the tetrasubstituted furan 22. In fumaronitrile, electrophilicity and steric
demand are diminished, and a 1,3-cycloaddition produces the 4,5-dihydro-1H-pyrazole derivative 25. The
reaction of 4 with dimethyl acetylenedicarboxylate leads to pyrazole 29 þ isobutene.
1. Introduction. – 1,3-Dipoles are ambiphilic by definition [2a]. The predominant
reactivity allows their classification into nucleophilic, nucleophilic – electrophilic, and
electrophilic 1,3-dipoles. In the framework of the MO-perturbation theory (PMO), the
three classes correspond to different contributions of the HOÀLUinteractions
between the cycloaddition partners to the energy of the transition structure (TS)
[2b][3] (for reviews, see [4][5]).
Methyl diazoacetate (1) is a 1,3-dipole with well-balanced nucleophilicity and
electrophilicity; i.e., 1 undergoes cycloadditions with electrophilic (a,b-unsaturated
carbonyl compounds and nitriles) and nucleophilic dipolarophiles (enamines, yn-
amines) [1][6]. Whereas dimethyl diazomalonate (2) and methyl diazo(phenylsulfo-
nyl)acetate (3) move towards electrophilic 1,3-dipoles on the continuous scale [6],
diazomethane, higher diazoalkanes, and phenylated diazomethanes are nucleophilic
1
)
)
)
1,3-Dipolar Cycloadditions, Part 136; Part 135: [1].
Present address: DMS Fine Chemicals, Austria GmbH, St. Peterstrasse 25, A-4021 Linz.
2
3
´
´
Present address: University of Łodz, Section of Heteroorganic Compounds, Narutowicza 68, 90-136
´
´
Łodz, Poland.
ꢂ 2007 Verlag Helvetica Chimica Acta AG, Zürich

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1,3-dipoles. Diazomethane no longer reacts with enamines, but the increase of the
cycloaddition rate by electron-attracting substituents in the ethylenic dipolarophile is
dramatic: ethyl acrylate reacts 107 times faster than butyl vinyl ether (DMF, 258), and
the cycloadditions with dimethyl fumarate or dimethyl acetylenedicarboxylate are
beyond the range of conventional rate measurements [7][8].
A switch from concerted cycloaddition to a two-step pathway was observed when
two conditions were fulfilled: a great difference in nucleophilicity and electrophilicity
between the reactants, and steric hindrance at least at one terminus of the 1,3-dipole.
Such a change of mechanism has been studied for cycloadditions of thiocarbonyl ylides
[9] (for a review, see [10]) and sulfonyl azides [11][12]. A similar cooperation of steric
and electronic effects is described here for cycloadditions of di(tert-butyl)diazo-
methane (4).
The chemistry of 3-diazo-2,2,4,4-tetramethylpentane (4) is not nearly as developed
as the reaction profile of diazomethane. The bulky 4 was first prepared by Barton et al.
and served as a building block in the synthesis of overcrowded ethylenes [13][14].
Thermolysis of 4 at 1358 furnished the cyclopropane derivative 5 (84%) [14], a
CH-insertion product, that suggests the intermediacy of di(tert-butyl)carbene. Under
varied conditions (presence of Se and Bu3N), the branched alkene 6 was the major
product (32%) [14].
Bock et al. studied the conversions of 4 in a flow system above 600 K at 10À2 mbar
on the surface of metal catalysts [15]. The ratio of the produced hydrocarbons 5 – 7
varied with the nature of the catalyst, and ꢀchemisorbed di(tert-butyl)carbeneꢁ was
assumed responsible. Both radical cation and radical anion of 4 appear to lose N2
rapidly [15]. We are not aware that reactions of 4 with Brønsted acids have been
studied. Cycloadditions of 4 with thiones gave rise to 2,5-dihydro-1,3,4-thiadiazoles 8
[13][16].
2. Results and Discussion. – 2.1. Formation and Structure of1:2 Products with (E)-
BTE. Like ethenetetracarbonitrile, (E)- and (Z)-1,2-bis(trifluoromethyl)ethene-1,2-

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dicarbonitrile (¼(E)- and (Z)-2,3-bis(trifluoromethyl)but-2-enedinitrile), abbreviated
as (E)-BTE and (Z)-BTE, are highly reactive tetra-acceptor-substituted ethylenes
[17]. They beautifully serve as stereochemical probes in mechanistic investigations. It
has recently been demonstrated that the 1,3-dipolar cycloadditions of methyl
diazoacetate (1) to (E)- and (Z)-BTE proceed with retention of dipolarophile
configuration (> 99.93% and > 99.8%, resp.) [1]. Retention is a necessary, though not
sufficient, criterion of concertedness.
When di(tert-butyl)diazomethane (4) was reacted with (E)-BTE (CH2Cl2; À 58 to
room temperature), not the usual dihydropyrazole was formed, but rather the
diastereoisomeric 1:2 products 9A and 9B (54%, A/B ca. 60 :40) were isolated
(Scheme 1); the elemental analyses and an m/z value of 554 left no doubt about the
molecular formula. The diastereoisomeric cyclopentenes 9A and 9B were separated by
preparative layer chromatography (PLC) and obtained crystalline.
Scheme 1
In the 19F-NMR spectrum of the diastereoisomer mixture (Fig. 1), the integrals
disclose the ratio 9A/9B, and the chemical shifts underline the structural relation,
whereas the splitting pattern of the signals allows the configurational assignment. The
F,F-coupling constants and the multiplicities enable the allocation of the four CF3
groups.
The downfield quadruplets, d À 56.65 for 9A and À 56.50 for 9B, belong to
CF3ÀC(5) which are located at a sp2-hybridized C-atom. The coupling partner,
CF3ÀC(1), resonates at À 67.23 (A) and À 66.72 (B), and these signals appear in Fig. 2
as a nonadecet for A and a decet for B, both with equidistant lines.
When rotation about the bond CF3ÀC is fast on the NMR time scale, the three F-
atoms are isochronous, and the coupling with a second CF3 group leads to two
quadruplets with equidistant lines; the heights (1:3 :3 :1) are determined by the
binomial coefficients. Not at all surprisingly, sets of binomial coefficients in the
presence of several coupling partners can cooperate to afford simple patterns with
equidistant lines, provided the J values are multiples of the lowest one, and the spectra
are of first-order. The CF3ÀC(1) in 9A couples with the other three CF3 groups with
J ¼ 3.0, 6.0, and 8.9 Hz; the small deviation of the last value from 9.0 leads to a tiny
increase of line width. Coincidence of lines reduces a formal system of 64 lines (qqq) to
nineteen lines (Fig. 2, left). The two 5J parameters of CF3ÀC(1) in 9B, 6.4 and 12.8 Hz,
are multiples, too, and the quadruplet of quadruplets is simplified to ten equidistant

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lines (Fig. 2, right). The heights of the lines are virtually identical with those calculated
by the binomial superposition of types 1:3 :3 :1. Of course, the appropriate coupling
constants emerge again in the signals of CF3ÀC(2) and CF3ÀC(3).
F,F Coupling is predominantly transmitted through space, and Jcis,vic > Jtrans,vic is
expected for CF3 groups in five-membered rings. In the dihydro-1H-pyrazole from
methyl diazoacetate and (E)-BTE, Jtrans,vic ¼ 0 was found [1]. Van der Waals strain in the
persubstituted cyclopentenes 9 probably distorts the regular half-chair conformation,
i.e., substantial values of Jtrans,vic were observed (Fig. 1). Sterically hindered 3,4-
bis(trifluoromethyl)spirothiolanes showed Jtrans,vic ¼ 4.1 – 11.6 Hz, but Jcis,vic was always
somewhat larger [18].
It is only in 9A that CF3ÀC(1) couples with CF3ÀC(3), i.e., across the ring;
6J(1,3) ¼ 3.0 Hz establishes a cis-relation of these CF3 groups and allows the structural
assignment of 9A and 9B. The atom C(2) is another stereogenic center; could a formal
(Z)-BTE unit be built into the five-membered ring? The coupling network finds in 9A
and 9B the best solution by far; it is buttressed by the largest constant (5J(1,2) ¼ 12.8 Hz
in 9B) for the sole cis,vic-coupling. One more argument: the CF3ÀC(2) groups in 9A
and 9B exhibit the greatest difference in chemical shifts (2.0 ppm). Previous experience
reveals that cis,vic-CF3 generates a greater downfield shift than cis,vic-CN. The
CF3ÀC(2) has a cis,vic-CF3 group in 9B, but not in 9A.
The 13C-NMR spectra are in accordance with 9A and 9B, and the C,F couplings,
2J ¼ 29 – 37, are helpful in the assignments. Thus, the quadruplets at d 84.8 (9A) and 82.1
(9B) must belong to C(5), i.e., the enamine b-position, whereas the singlets of C(4) are
found at 142.1 and 139.7. The imino C-atoms resonate at d 192.8 (A) and 191.8 (B).
Furthermore, the X-ray-analysis of 12B (see below) indirectly confirms the structure 9.
2.2. Interception ofIntermediate 10. The formation of the 1:2 product 9 passes at
least one intermediate by necessity. Structure 9 suggests that it is the CN group of (E)-
BTE and not the electrophilic C-atom which attacks the highly hindered C-atom of
diazoalkane 4. The assumed zwitterionic intermediate 10 is illustrated in Scheme 2 by
three resonance structures. Formula 10c reveals a nitrile ylide, a 1,3-dipole; the
cycloaddition of the second molecule of (E)-BTE to yield a dihydro-3H-pyrazole is
prevented by the voluminous t-Bu groups. The charge distribution in 10b does not fit an
ꢀclassicalꢁ 1,3-dipole, but symbolizes the pathway by which the stepwise addition of the
second (E)-BTE could furnish the persubstituted cyclopentenes 9.
Our attempts of trapping intermediate 10 by a third reagent were successful with
dimethyl 2,3-dicyanofumarate (¼dimethyl (E)-2,3-dicyanobut-2-enedioate; 11). It
turned out that (E)-BTE is faster than 11 in the initial reaction with diazo compound 4,
whereas 11 exceeds (E)-BTE in its readiness to combine with intermediate 10. When
(E)-BTE (0.7 mmol) was slowly introduced into the deep-blue mixture (CT complex)
of 4 and 11 (1.0 mmol each) in CH2Cl2 at room temperature, 19F-NMR analysis
indicated the 1:1:1 product 12 (45%) in two diastereoisomers, A/B 57:43, and little
9A þ 9B. Remarkably, half of (E)-BTE – applied in less than the stoichiometric amount
– remained unreacted. The liberation of 1.0 mmol of N2 suggests a catalytic
decomposition of 4 which competes with the adduct formation (see Sect. 2.3).
Layer chromatography allowed a partial separation of the diastereoisomer mixture.
The minor component 12B was obtained pure and crystalline; the spectra of 12A were
determined by the difference method. The 19F-NMR quadruplets of 12B at À 57.88 and

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Scheme 2
À 65.12 ppm with 5J(F,F) ¼ 7.7 Hz are separated from those of 12A which couple with
8.2 Hz. The 13C-NMR spectrum of 12B exhibits a similarly polarized C¼C bond as 9B:
d 81.6 for C(4) and 146.0 for C(3) of 12B vs. 82.1 for C(5) and 139.7 for C(4) of 9B.
The X-ray diffraction analysis (Fig. 3 and Table) reveals a cis,trans-structure for 12B
(and by exclusion, trans,trans for 12A). As expected, the cyclopentene ring appears in
an envelope conformation with C(4) (crystallographic atom numbering as shown in
Fig. 3) as the flap; C(4) is located 0.41 Š below the plane of the other four C-atoms.
Due to a twist angle of 89.48 at the central bond, the system C(13)¼N(1)ÀC(1)¼C(2)
lacks p-conjugation, probably as a consequence of steric constraints. Van der Waals
strain is likewise responsible for the stretching of the CÀC bonds: 1.601 Š for
C(3)ÀC(4) and 1.581 Š for C(4)ÀC(5).
2.3. Competing Reactions and Mechanistic Considerations. In the reaction of di(tert-
butyl)diazomethane (4) with (E)-BTE, part of the latter remained unconsumed, even
when applied much below the 1:2 stoichiometry required for the formation of 9
1
(Scheme 1). The N2 volume liberated and the H-NMR spectrum showed that 4 was
always completely consumed. Thus, the formation of 9 competed with a decomposition
of 4, which afforded 7 þ N2 and was catalyzed by (E)-BTE.
The rate ratio for the formation of 9 and the (E)-BTE-catalyzed dediazoniation of
4 determines the yield of 9; the yield fluctuated. When, two years after the original
study, another experimentalist repeated the reaction with newly prepared reagents, the
yield of 9A þ 9B (64 :36) dropped to 2.5%, and 89% of 2,3,4,4-tetramethylpent-1-ene
(7) was obtained. The blue-violet CT color now disappeared even at À 458 within

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Fig. 3. X-Ray crystal structure ofthe 1:1:1 product 12B (ZORTEP plot; thermal ellipsoids represent
30% probability)
Table. X-Ray Structure ofCyclopentene Derivative 12B: Selected Bond Lengths and Angles (position
numbering from Fig. 3; standard deviations in parentheses)
Bond length [Š]
Angle [8]
C(1)¼C(2)
C(2)ÀC(3)
C(3)ÀC(4)
C(4)ÀC(5)
C(5)ÀC(1)
C(1)ÀN(1)
N(1)¼C(13)
F3C(6)ÀC(2)
F3C(7)ÀC(3)
1.347(3)
1.517(3)
1.601(3)
1.581(3)
1.531(3)
1.332(2)
1.266(2)
1.482(3)
1.551(3)
C(5)ÀC(1)ÀC(2)
C(1)ÀC(2)ÀC(3)
C(2)ÀC(3)ÀC(4)
C(3)ÀC(4)ÀC(5)
C(4)ÀC(5)ÀC(1)
C(1)ÀN(1)ÀC(13)
111.2(2)
113.1(2)
102.6(2)
103.4(2)
103.5(1)
147.8(2)
minutes, and N2 was evolved; in the absence of (E)-BTE, 4 is stable at room
temperature and distillable. Not reproducible yields are an embarassment for the
experimentalist and reveal that not all parameters are under control. In search of an
unknown co-catalyst, our first guess was an electron-transfer process induced by a trace
of metal; it did not find experimental confirmation.
According to McGarrity and Cox, diazomethane is protonated by superacid at C-
and N-atom in the ratio 71:29 (FSO3H/SbF5, À 1278, kinetic control) [19]. Two of the
four initial interactions of (E)-BTE with 4 are worth consideration. In di(tert-
butyl)diazomethane (4), C-attack by electrophilic reagents should be retarded, but the

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CN N-atom of (E)-BTE may still be capable of piercing through the di(tert-butyl)
shield and give rise to the diazonium zwitterion 13 (Scheme 3). Loss of N2 affords
intermediate 10, suggested above as the precursor of products 9 and 12.
Scheme 3
Attack by the C-atom of (E)-BTE on the terminal N-atom of 4 would furnish
zwitterion 14. Conceivably, a cyclization of 14 affords the seven-membered cyclic
ketene imine 15, and subsequent elimination of N2 would offer a second pathway to
zwitterion 10. An analogy to the 1,7-cyclization: the zwitterions, which are formed from
thiocarbonyl ylides and (E)-BTE, furnish isolable cyclic seven-membered ketene
imines [18][20].
The loss of N2 may also occur on the level of 14, after a Me shift generated the
tertiary carbocation 16. The recovery of (E)-BTE in the ensuing fragmentation
warrants the catalytic character of this decomposition mode of 4. However, this
pathway should lead to 2,3,4,4-tetramethylpent-2-ene (6), whereas the isolated
hydrocarbon is the pent-1-ene derivative 7 (purity > 95%).
Pentene 7 is expected, when the catalytic role is ascribed to the proton (Scheme 4).
Interestingly, (E)-BTE is more sensitive to H2O and alcohol than ethenetetracarboni-
trile (TCNE); the latter can be recrystallized from MeOH at low temperature.

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Conceivably, a trace of H2O converts BTE to 17, which might be sufficiently acidic for
the protonation of 4. The diazonium ion 18 loses N2, and the carbocationic
rearrangement follows known principles (review: [21]). When the Me shift occurs in
concert with the cleavage of the CÀN bond, the secondary carbocation 19 would not be
required as an intermediate. In the deprotonation of the tertiary carbocation 20 by the
diazoalkane 4, the methyl H-atom is strongly preferred to the H-atom at the tertiary
center – for obvious steric reasons –, thus paving the way to the thermodynamically less
stable olefin 7.
Scheme 4
Are adventitious traces of H2O in the reaction of 4 with (E)-BTE responsible for
the catalytic decomposition of 4? The assumption was nurtured by the observation that
the addition of 1 equiv. of H2O to the reaction system at low temperature induced rapid
fading of the deep CT color and evolution of N2. The original experiments were carried
out with a sample of 4, which was prepared by thermolysis (80 – 1008) of the dry lithium
salt of di(tert-butyl) ketone tosylhydrazone. For the later rework, 4 was obtained from
the oxidation of di(tert-butyl) ketone hydrazone with nickel peroxide, described by
Mloston et al. [16], and some humidity may have escaped removal.
A test experiment revealed that a sample of di(tert-butyl)diazomethane (4),
prepared by the nickel peroxide method and distilled, still showed a small IR
absorption of H2O. When its solution in CDCl3 was treated with a small amount of
H2SO4 at room temperature, N2 was evolved, and the 1H-NMR analysis indicated 91%
of pentene 7, free of isomer 6.
2.4. Reactions with Further Electrophilic Multiple Bonds. Diazoalkane 4 and
dimethyl 2,3-dicyanofumarate (11) gave a deep-blue CT complex, and the reaction with
N2 evolution took place at 0 – 208. The product C17H24N2O4 was obtained pure by
distillation and corresponded to 4 þ 11 À N2. The intermediate 21 (Scheme 5), an
analogue of 10, attained stabilization by intramolecular nucleophilic addition and
furnished the tetrasubstituted furan 22. Among several structures discussed, 22 fits the
13C-NMR spectrum best.
The yield of isolated pure 22 amounted to 40%, but the elimination of N2 from 4
was complete. Again, the highly electrophilic 11 catalyzed the conversion 4 ! 7 þ N2 in
the presence of some H2O, as shown above for (E)-BTE; the ratio of furan 22 and
alkene 7 was likewise fluctuating.
In a preliminary experiment, 4 was reacted with (E)-BTE and dimethyl 2,3-
dicyanomaleate (23); two new products, with two CF3 groups each, require further
study.
Fumaronitrile (24) is less electrophilic than 11 and has lower steric demands. 1,3-
Dipolar cycloaddition with 4 afforded the 4,5-dihydro-1H-pyrazole derivative 25

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Scheme 5
(83%). The IR NH absorption and the 13C-NMR parameters are in accordance with the
structure 25.
Dimethyl acetylenedicarboxylate is strongly electrophilic, but of low steric demand,
in the cycloaddition process. Its reaction with 4 at À 208 furnished dimethyl 5-(tert-
butyl)pyrazole-3,4-dicarboxylate (29; 58%) and an equivalent amount of isobutene.
1H-NMR Monitoring (À208, CDCl3) revealed an intermediate which could be – but
need not be – the 3H-pyrazole 26. An initially formed zwitterion 27 could either
undergo ring closure to give 26, or induce the elimination of isobutene by its
carbanionic terminus and provide 28 as an open-chain intermediate. The pyrazole 29
would emerge from a pentadienyl-anion type electrocyclization of 28. Pyrazole 29 was
independently synthesized by the reaction of 1-diazo-2,2-dimethylpropane (ꢀdiazo-
neopentaneꢁ) with dimethyl acetylenedicarboxylate.
We thank cand. chem. Marion Jurk and cand. chem. Thomas Ruhland for skilled experimental co-
operation. The Fonds der Chemischen Industrie, Frankfurt, deserves our gratitude for support. Our
thanks are going to Helmut Huber for his help in NMR spectroscopy, to Reinhard Seidl for recording the
mass spectra, and to Helmut Schulz and Magdalena Schwarz for the elemental analyses.

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Experimental Part
1. General. For instruments and procedures, see [1].
2. Starting Materials. 2.1. 3-Diazo-2,2,4,4-tetramethylpentane (4): [13]. Instead of the sodium salt of
2,2,4,4-tetramethylpentan-3-one tosylhydrazone, the dry lithium salt was thermolyzed at 80 – 1008/
0.1 Torr, and 4 was condensed in a cold trap at À 788; orangered liquid, 46% crude product, 39% after
redistillation at 50 – 518/12 Torr.
2.2. (E)- and (Z)-1,2-Bis(trifluoromethyl)ethene-1,2-dicarbonitrile ((E)- and (Z)-BTE): [17][22].
2.3. Dimethyl 2,3-Dicyanofumarate (11): [23]; 2,3-Dimethyl Dicyanomaleate (23): [24].
3. Reactions of 1 with (E)-BTE. 3.1. Isolation of 9A þ 9B. The soln. of 4 (159 mg, 1.03 mmol) in abs.
CH2Cl2 (0.5 ml) was dropwise added to (E)-BTE (216 mg, 1.01 mmol) in CH2Cl2 (1 ml), and the mixture
was magnetically stirred at À 48. The blue-violet color (CT complex) changed on slow warming to r.t. via
red-violet to light-yellow, while N2 was evolved. After evaporation of the solvent, the residue was
subjected to column chromatography (CC) on silica gel with CH2Cl2/pentane 1:1. The fraction with Rf
0.75 – 0.89 was eluted with CH2Cl2 and furnished, after concentration and recrystallization from pentane
at À 188, the anal. pure 1:2 adducts 9 (150 mg, 54%; 9A/9B ca. 60 :40). 19F-NMR: Fig. 1. MS (408): 554
(1, Mþ), 535 (1, [M À F]þ), 497 (6, [M À t-Bu]þ), 471 (1, [497 À CN]þ), 429 (0.3, [497 À CF3 þ H]þ), 327
(0.5), 284 (0.5), 214 (0.5, BTEþ), 69 (0.4, CF3þ), 57 (100, t-Buþ), 41 (16, [allyl]þ). Anal. calc. for
C21H18F12N4 (554.39): C 45.49, H 3.27, N 10.11; found: C 45.75, H 3.23, N 10.06.
The separation of the diastereoisomers succeeded by PLC with Et2O/light petroleum 1:20, 8 ꢀ
development. Elution with CH2Cl2 and crystallization from pentane afforded 9B/9A 95 :5 from the first
fraction and pure 9A from the second fraction.
3.2. trans,trans-4-{[1-(1,1-Dimethylethyl)-2,2-dimethylpropylidene]amino}-1,2,3,5-tetrakis(trifluoro-
methyl)cyclopent-4-ene-1,2,3-tricarbonitrile (9A). M.p. 578. UV (CHCl3): 260 (4.22), 306 (3.12). IR
(KBr): 670m, 727m, 729m, 825m, 968m; 1134s, 1203vs, 1223vs, 1237vs, 1264s (CÀF stretch.); 1355s; 1563s
1
(C¼N); 1775s (br.) (C¼C?); 2255vw (CꢁN). H-NMR (80 MHz): 1.3, 1.4 (2s, 2 ꢀ 3 Me). 13C-NMR
(50.3 MHz, H-decoupled, J(C,F) couplings, 3J(C,F) unresolved): 29.8 (s, 3 Me); 30.4 (s, 3 Me); 46.2, 47.2
(2s, 2 Me3C); 3q of C(1), C(2), C(3): 55.0 (2J ¼ 29.8), 57.5 (2J ¼ 33.5), 59.8 (2J ¼ 30.5); 84.8 (q, 2J ¼ 34.1,
C(5)); 107.7, 109.4, 109.8 (3s, 3 CN); 4q of 4 CF3: 121.08 (1J ¼ 289.8), 121.22 (1J ¼ 287.4), 121.32 (1J ¼
282.8), 121.46 (1J ¼ 282.1); 142.1 (s, C(4)); 192.8 (s, C(2’)). 19F-NMR (376.3 MHz, d based on CF3OPh
as secondary standard (À 58.38)): Figs. 1 and 2.
3.3. trans,cis-Isomer 9B. M.p. 79 – 81. UV (CHCl3): 254 (4.17), 305 (3.23). IR (KBr): 667m, 717m,
824m, 1046m; 1140s, 1183vs, 1215vs (br.), 1269m, 1345s (CÀF stretch.); 1583s (C¼N); 1751, 1762s (br.)
(C¼C?); 2255vw (CꢁN). 1H-NMR (80 MHz): 1.3, 1.4 (2s, 2 ꢀ 3 Me). 13C-NMR (50.3 MHz, H-
3
decoupled, coupling constants J(C,F); J(C,F) unresolved): 29.47, 29.63 (2s, 2 ꢀ 3 Me); 45.60, 46.70 (2s,
2 Me3C); 3q of C(1), C(2), C(3): 56.7 (2J ¼ 31.7), 57.8 (2J ¼ 34.7), 58.7 (2J ¼ 33.2); 82.1 (q, 2J ¼ 36.2,
C(5)); 108.1, 108.7, 109.9 (3s, 3 CN); 4 q of 4 CF3: 119.73 (1J ¼ 288.4), 120.66 (1J ¼ 289.9), 121.02 (1J ¼
272.2), 121.46 (1J ¼ 288.9); 139.7 (s, C(4)); 191.8 (s, C(2’)). 19F-NMR (376.3 MHz, d based on CF3OPh):
Figs. 1 and 2.
3.4. 19F-NMR Monitoring. The deep-blue-violet soln. of (E)-BTE (58.3 mg, 0.27 mmol) and 4
(34 mg, 0.22 mmol) in CD2Cl2 (0.55 ml) in the NMR tube at À 108 required 4 h for complete reaction.
The analysis showed (9A þ 9B)/(E)-BTE 71:29, a trace of (Z)-BTE, and some small unidentified
signals. Thus, part of BTE remained unconsumed despite an insufficient concentration for bisadduct
formation. According to the 1H-NMR spectrum, no 4 was left.
3.5. Competing Reactions of 4 with (E)-BTE. The fluctuations in the yield of the 1:2 products 9 were
mentioned in Sect. 2.3. One of the experiments with moist 4 [16] and isolation of pentene 7 is described.
(E)-BTE (2.20 mmol) in CDCl3 (0.7 ml) was introduced into the soln. of 4 (1.10 mmol) in CDCl3 (0.5 ml)
at À 58. The blue color was visible only for seconds, and N2 (24 ml) evolved without delay. Part of the
unreacted (E)-BTE crystallized from the pale-yellow soln. At r.t., PhOCF3 (0.564 mmol) and 1,1,2,2-
tetrachloroethane (0.586 mmol) were added as weight standards for 19F- and 1H-NMR analysis:
17.2 mmol (1.6%) of 9A and 10.1 mmol (0.9%) of 9B (A/B 64 :36), and 0.98 mmol (89%) of the C9-alkene
7. The solvent was removed by distillation over a small Vigreux column, and 2,3,4,4-tetramethylpent-1-ene
1
(7; 98 mg, 78%) was distilled from a microflask at 120 – 1238. The H- and 13C-NMR spectra are in full

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995
agreement with those described by Rüchardt and co-workers [25] for a specimen of 7 which was obtained
from 2,2,4,4-tetramethylpentan-3-ol with HMPT (3 h, 2208) [26]. The parameters of the 1H-coupled
13C-NMR spectrum (100.6 MHz; J(C,H) are given here): 15.02 (dq, 2J ¼ 4.6, 1J ¼ 125.5, MeÀC(3)); 22.61
(ddq, 3J ¼ 3.6, 4.8, 1J ¼ 125.5, MeÀC(2)); 28.17 (qm, 10 lines resolved, 1J ¼ 124.8, diastereotopic Me of t-
2
1
1
3
Bu); 33.1 (d, J ¼ 3.8, C(4)); 50.68 (d, J ¼ 123.9, C(3)); 111.86 (t of quint., J ¼ 154.2, J ¼ 6.0, C(1));
149.25 (s with fine splitting, C(2)). The 1H-NMR spectrum showed unidentified signals at 0.9 – 1.9 ppm,
less than 5%; the only 13C-NMR signals of olefinic C-atoms were those of 7.
A corresponding experiment with (Z)-BTE gave similar results; the unreacted BTE had reached
equilibrium, (E)/(Z) 94 :6.
3.6. Variation ofConditions. Freshly distilled 4 (1.0 mmol) [16] and freshly sublimed (E)-BTE
(0.5 mmol) in CH2Cl2 (1.0 ml) afforded a blue-violet soln. at À 408; the CT color disappeared in some
min, and N2 was liberated (23 ml). The 19F-NMR analysis showed 8.9 mmol (3.6%) of 9A þ 9B. Another
experiment was carried out in the presence of benzophenone (20 mol-%); the violet color was stable at
À 458 for 40 min, but, below 08, the N2 evolution set in, and the color changed to yellow; NMR analysis:
8.3% of 9, A/B 64 :36. Experiments in the presence of 1,4-dinitrobenzene or di(tert-butyl)nitroxyl
furnished 3 – 4% of 9. In a further experiment, H2O (1.0 mmol) was added to the blue-violet soln. of 4 þ
(E)-BTE at À 408; the deep color rapidly turned to light-yellow, and no 9 was found.
3.7. Acid-Catalyzed Decomposition of 4. Di(tert-butyl) ketone hydrazone was oxidized with nickel
peroxide [16][27][28]. After distillation of 4 from a microflask at 408/8 – 10 Torr, the IR absorption at
3330 cmÀ1 was attributed to a trace of H2O. When CDCl3 is shaken with some drops of 98% H2SO4 and
allowed to settle for 3 h, the clear supernatant phase was carefully pipetted and is 5 – 7 mm in H2SO4
[29][30]. A weighed amount of 4 was reacted with the mentioned CDCl3 soln. (0.5 ml) in an NMR tube;
the N2 evolution at r.t. terminated after 15 min. The 1H-NMR analysis with sym-C2H2Cl4 as weight
standard indicated 90% of 7 (¼CH2 at 4.60 – 4.83 ppm).
4. Reaction of 4 with (E)-BTE and Dimethyl 2,3-Dicyanofumarate (¼ Dimethyl (E)-2,3-Dicyanobut-
2-enedioate; 11). 4.1. Isolation of1:1:1 Adducts . Diazo compound 4 (162 mg, 1.05 mmol) and (E)-BTE
(169 mg, 0.79 mmol) were combined in CH2Cl2 (3 ml) at À 358 and slowly introduced into the stirred
suspension of 11 (204 mg, 1.05 mmol) in CH2Cl2 (4 ml) at 08; 11 dissolved within several min. The N2
evolution started, and the deep color faded, when the cooling bath was removed, and r.t. was reached.
After adding PhCCl2CF3 (d(F) À 78.27) as weight standard, the 19F-NMR analysis (in % of applied BTE)
indicated unconsumed (E)-BTE (439 mmol, 56%, d À 62.26), a trace of (Z)-BTE (À 59.2), the mixed
cycloadducts 12 (266 mmol, 34%, two diastereoisomers A/B 57:43), and 9A/9B (41 mmol, 10%). PLC
(silica gel; light petroleum/Et2O 3 :1) gave five fractions. The third fraction (Rf 0.67 – 0.73) furnished the
pure minor adduct 12B. Isomer 12A was in the second fraction (Rf 0.3 – 0.4), but was not obtained pure
(19F-NMR in CDCl3: À 57.23, À 66.19 (2q, J(F,F) ¼ 8.2)). The fourth fraction contained 9A þ 9B.
4.2. Improved Procedure. In a second experiment, 4 (1.0 mmol) and 11 (1.0 mmol) in CH2Cl2 (8 ml)
were stirred in a bath at r.t.; when (E)-BTE (0.75 mmol) in CH2Cl2 (1 ml) was added in some min,
decolorization of the blue-violet soln. was observed, and N2 (22 ml) was liberated. The 19F-NMR analysis
(as above) showed 50% unconsumed (E)-BTE and 45% of 12.
4.3. Dimethyl (1RS,2RS,5RS)-1,2,5-Tricyano-3-{[1-(1,1-dimethylethyl)-2,2-dimethylpropylidene]-
amino}-4,5-bis(trifluoromethyl)cyclopent-3-ene-1,2-dicarboxylate (12B). Colorless crystals from CH2Cl2/
pentane; m.p. 1408 after sintering (modification change) at 1158. IR (KBr): 974m; 1123m (br.), 1178s,
1223s, 1247vs (br., CÀF); 1352m; 1583m (br., C¼N); 1772vs, 1755 (sh), 1730 (C¼O, C¼C). 1H-NMR:
1.22 (s, 3 Me); 1.33 (s, 3 Me); 3.95, 4.03 (2s, 2 MeO). 13C-NMR (20.2 MHz, 1H-decoupled): 29.9 (s, 3 Me);
30.9 (s, 3 Me); 44.8, 46.9 (2s, 2 Me3C); 53.5, 62.9 (2s, C(1), C(2)); 55.68, 56.11 (2s, 2 MeO); 60.2 (q, 2J ¼ 33,
C(5)); 81.6 (q, 2J ¼ 36, C(4)); 111.0, 111.6 (2s, 3 CN); 120.72 (q, 1J ¼ 287, CF3); 120.94 (q, 1J ¼ 277, CF3);
146.0 (s, C(3)); 159.8, 160.8 (2s, 2 C¼O); 189.8 (s, C(2’)). 19F-NMR (94.2 MHz): À 57.88, À 65.12 (2q,
5J(F,F) ¼ 7.7, 2 CF 3). MS (708): 534 (3, Mþ), 519 (1, [M À Me]þ), 515 (1, [M À F]þ), 502 (0.7, [M À
MeOH]þ), 477 (41, [M À C4H9]þ), 452 (0.7), 419 (1.2, [M À CO2Me À C4H8]þ), 392 (1), 292 (1), 69 (1,
[CF3]þ), 57 (100, [C4H9]þ), 56 (4, [C4H8]þ), 41 (17, [allyl]þ). Anal. calc. for C13H24F6N4O4 (534.45): C
51.68, H 4.53, N 10.48; found: C 52.15, H 4.58, N 10.29.
4.4. X-Ray Diffraction Analysis of 12B (Fig. 3 and Table). The crystal was sealed in a glass capillary
and mounted on the goniometer head of a CAD4 diffractometer operating with MoKa radiation

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(l ¼ 0.71069 Š) and graphite monochromator. Unit cell dimensions: a ¼ 29.438(6) Š, b ¼ 18.467(4) Š,
c ¼ 9.205(2) Š, a ¼ b ¼ g ¼ 908; V¼ 5004.5 Š3, Z ¼ 4, Dcalc. 1.419 mg/mm3, F(000) ¼ 2160, T¼ 293 K, m ¼
0.127 mmÀ1. The unit cell dimensions resulted from a least-squares fit of 25 centered reflections, w À 2q
scan; q range 2.21 – 24.978 for all ꢂ h, ꢂ k, ꢂ l reflections, 3581 reflections collected, 2706 with I > 2s
(I). The structure was solved by the SHELXS-86 program and refined with SHELXL-93 [31] with
goodness-of-fit ¼ 1.060. Final R1 ¼ 0.0320 and wR2 ¼ 0.0985 for reflections with I > 2s(I); R1 ¼ 1.0597 and
wR2 ¼ 0.1047 for all data. Maximum and minimum of the final difference Fourier synthesis were 0.197
and À 0.137 eŠ3. Non-H-atoms were refined anisotropically, H-atoms isotropically. The final difference
map was featureless with 345 refined variables; ZORTEP plot was generated according to [32]. The
deposition No. CCDC-297357 contains supplementary data which can be obtained from the Cambridge
Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB21EZ, UK (e-mail: depos-
it@ccdc.cam.ac.uk).
4.5. Reaction of 4 with (E)-BTE and Dimethyl 2,3-Dicyanomaleate (¼ Dimethyl (Z)-2,3-
Dicyanobut-2-enedioate; 23). The violet soln. of 4 (72 mg, 0.47 mmol) and (E)-BTE (92 mg, 0.43 mmol)
in CDCl3 (2 ml) was dropwise added to 23 (97 mg, 0.50 mmol) in CH2Cl2 (2 ml) at r.t.; the color
disappeared, and N2 evolved. With PhCCl2CF3 as weight standard, the 19F-NMR analysis (94.2 MHz)
indicated unchanged (E)-BTE (0.281 mmol, 65%), new products in diastereoisomers D and E
(0.135 mmol, 31%; D/E 73 :27), and 9 (0.006 mmol, 1.3%). Product D: d(F) À 57.80, À 65.53 (2q, 5J ¼
5
8.1); product E: À 57.48, À 67.86 (2q, J ¼ 8.5). The separation of D and E by PLC was not achieved.
5. Reaction of 4 with Dimethyl 2,3-Dicyanofumarate (11). 5.1. Methyl 4-Cyano-5-methoxy-2-{[1-(1,1-
dimethylethyl)-2,2-dimethylpropylidene]amino}furan-3-carboxylate (22). When 4 (156 mg, 1.0 mmol) in
CH2Cl2 (0.5 ml) was added to the magnetically stirred suspension of 11 (194 mg, 1.0 mmol) in CH2Cl2
(5 ml) at 08, the deep-blue color of the CT complex was stable. The N2 evolution started after removal of
the cooling bath and was complete (25 ml) after 5 h at 208. The solvent was distilled i.v., and the brown
residue was digested with little CDCl3; the undissolved excess of 11 was filtered. Bulb-to-bulb distillation
at 1408/0.1 Torr gave anal. pure 22 (127 mg, 40%). Viscous yellow oil. IR (film): 980m; 1087s, 1123m,
1226s, 1284m, 1338s (CÀO of ester and ether); 1555m (C¼N); 1624s, 1636s, 1685vs (arom. ring vibr.),
1718s (C¼O); 2229m (CꢁN). 1H-NMR (400 MHz): 1.31 (s, 6 Me); 3.77 (s, MeO, ether); 4.15 (s, MeO,
ester. 13C-NMR (100.6 MHz, 1H-decoupled): 30.1 (6 Me); 44.8 (2 Me3C); 51.1, 59.7 (2 MeO); 70.8
(C(4)); 91.4 (C(3)); 113.0 (CꢁN); 150.9 (C(2)); 160.4, 161.8 (C(5), C¼O); 195.5 (C¼N). MS: 320 (10,
Mþ), 305 (3, [M À Me]þ), 263 (22, [M À C4H9]þ; 13C calc. 3.18, found 3.19), 249 (6), 207 (19, [M À
C4H9 À C4H8]þ; 13C 1.85/1.78), 111 (11), 69 (14), 57 (100, t-Buþ), 41 (24, [allyl]þ). Anal. calc. for
C17H24N2O4 (320.38): C 63.73, H 7.55, N 8.74; found: C 63.75, H 7.58, N 8.61.
5.2. Competition with Olefin Formation. The recovery of unconsumed 11 and the evolution of 100%
N2 suggest that a decomposition of 4, catalyzed by 11, competes with the formation of 22, as described in
Sect. 3.5 for (E)-BTE. In an experiment with moist 4 [16], the 1H-NMR analysis (sym-C2H2Cl4 as
standard) indicated 23% of 22 (2s at 3.77, 4.15) and 63% of 7 (2s at 4.65, 4.72). Dimethyl 2,3-
dicyanomaleate (23) is easily soluble in CH2Cl2 and produced the blue CT color with 4 at À 458; soon the
less soluble 11 precipitated. The reaction at 0 – 208 afforded 22 (17%) and alkene 7 (58%).
6. Diazo Compound 4 and Fumaronitrile (¼(E)-But-2-enedinitrile; 24). In the reaction of
4
(1.0 mmol) with 24 (2.0 mmol) in CDCl3 (2 ml) at r.t., the red color of 4 disappeared within 1 h, and N2
(4.0 ml, 16%) was liberated. The 1H-NMR analysis disclosed 5,5-di(tert-butyl)-4,5-dihydro-1H-pyrazole-
3,4-dicarbonitrile (25; 83%) and alkene 7 (16%). PLC on silica gel with CH2Cl2 provided 25 (174 mg,
75%). Colorless prisms. M.p. 252 – 2548 (dec.) after recrystallization from CH2Cl2/pentane. IR (KBr):
1179s, 1292m, 1376s, 1431s, 1475s; 1535s (C¼N); 2210s, 2248s (CꢁN), 3347vs (NÀH). 1H-NMR
(400 MHz): 1.15 (sharp s, 3 Me); 1.28 (br. s, 3 Me); 4.37 (s, HÀC(4)); 6.94 (br. s, NH; disappears on
1
1
shaking with D2O). 13C-NMR (100.6 MHz, H-coupled): 29.04 (br. q, J(C,H) ¼ 126.3, Me); 29.13 (q,
1J ¼ 126.4, 3 Me); 29.20 (q, 1J ¼ 126.3, 2 Me); 41.39 (dd, 1J ¼ 136.9, 4J ¼ 4.6 (possibly homoallyl coupling
with NH), C(4)); 41.53, 42.37 (2m, 2J ꢃ 4, 2 MeC); 84.78 (m, J small, C(5)); 112.59 (d, 2J ¼ 12.2, C(3) or
CNÀC(4)); 112.71 (s, CNÀC(3)); 115.46 (d, 2J ¼ 12.6, CNÀC(4) or C(3)). Anal. calc. for C13H20N4
(232.32): C 67.20, H 8.68, N 24.12; found: C 67.21, H 8.62, N 23.93.
7. Diazoalkane 4 and Dimethyl Acetylenedicarboxylate (DMAD). 7.1. 1H-NMR Monitoring. DMAD
(70 ml, 80.9 mg, 0.57 mmol) was injected (Hamilton syringe) into the soln. of 4 (98.4 mg, 0.48 mmol) in

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997
CDCl3 (0.6 ml) at À 608. Signals: d 1.19 (4); 1.17 (26 or 28); 1.28 (29); 1.69, 4.58 (isobutene); 0.86, 4.70
(7); due to overlap, the MeO region is not useful. After 30 min at À 208, 4 and the nearby s of 26 (or 28)
had equal heights, corresponding to 43% of the total integral for the sat. CH region; isobutene (22%) and
29 (20%) indicated the secondary products, and the s at 0.86 could belong to 7 (7%). After further 30 min
at À 208, the s of 26 (or 28) was only a shoulder of the s of 4 (15%). The signals of 4 and the intermediate
disappeared after 1 h at 208; 29 (58%) and isobutene (54%) showed the expected equivalence; the
integral of the olefinic CH of isobutene was nearly a third of the Me2 signal.
7.2. Isolation of 29. The red soln. of 4 (2.7 mmol) and DMAD (2.0 mmol) in CDCl3 (3 ml) slowly
decolorized at À 208. Work-up of the light-yellow soln. afforded dimethyl 5-(tert-butyl)pyrazole-3,4-
dicarboxylate (29). Colorless crystals. M.p. 1468. A sample prepared from ꢀdiazoneopentaneꢁ and DMAD
was identical in m.p. and spectra. IR (KBr): 1090m, 1165m, 1247m (br.), 1286m (CÀO); 1472m, 1506m,
1
1653w (pyrazole vibr.), 1734vs (C¼O); 3176w (br., NÀH assoc.), 3422m (br., NÀH free). H-NMR
(80 MHz): 1.26 (s, t-Bu); 3.77, 3.81 (2s, 2 MeO). 13C-NMR (25.15 MHz, H-decoupled): 29.1 (s, 3 Me);
32.4 (s, Me3C); 52.13, 52.40 (2s, 2 MeO); 112.8 (s, C(4)); 141.4, 153.3 (2s, C(3), C(5)); 161.9, 165.8 (2s, 2
C¼O). MS (608): 240 (20, Mþ), 225 (18, [M À Me]þ), 209 (17, [M À MeO]þ), 193 (100), 57 (2, [C4H9]þ).
Anal. calc. for C11H16N2O4 (240.25): C 54.99, H 6.71, N 11.66; found: C 55.28, H 6.73, N 11.36.
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Received February 12, 2007