Synthetic approaches to bicyclic diazenium salts

Article abstract of DOI:10.1021/jo101706h

Bicyclic diazenium salts have been prepared from α-chloroazo species via a Lewis acid-mediated intramolecular cycloaddition. An alternative, more direct, route to these salts by the reaction of hydrazones with dimethylsulfonium ditriflate is also describe

Full text of DOI:10.1021/jo101706h

pubs.acs.org/joc
Synthetic Approaches to Bicyclic Diazenium Salts
J. Wyman, M. I. Javed, N. Al-Bataineh, and M. Brewer*
Department of Chemistry, The University of Vermont, 82 University Place, Burlington, Vermont 05405,
United States
matthias.brewer@uvm.edu
Received September 1, 2010
Bicyclic diazenium salts have been prepared from R-chloroazo species via a Lewis acid-mediated
intramolecular cycloaddition. An alternative, more direct, route to these salts by the reaction of hydra-
zones with dimethylsulfonium ditriflate is also described. Terminal olefins provided mixtures of fused
and bridged bicyclic diazenium salts. The ratio of the fused and bridged species was observed to depend
on the electronics of the N-aryl substituent, which is explained by considering a concerted asynchro-
nous cycloaddition mechanism.
SCHEME 1. Nelsen’s Preparation of Bridged Bicyclic Diaze-
nium Salts
Introduction
Cyclic trisubstituted diazenium salts (e.g., 2, Scheme 1)
are cationic heterocycles that contain a reactive nitrogen-
nitrogen double bond.1 Although these species are poten-
tially useful synthetic intermediates, they have received less
attention from the synthetic community than most classes of
nitrogen-containing heterocycles and few methods exist for
their preparation. Nelsen and co-workers2-5 have prepared
bridged bicyclic diazenium salts by alkylation of the corre-
sponding diazene (Scheme 1), and have studied the redox
properties, structure, and charge distribution of these salts;
Nelsen and co-workers also observed that protonated bi-
cyclic azo compounds act as dienophiles in [4 þ 2] cycload-
dition reactions.6,7
SCHEME 2. Jochims’ Preparation of Diazenium Salts
More recently, Jochims and colleagues8-10 reported that
R-chloroazo compounds (e.g., 3, Scheme 2) react with halophilic
Lewis acids to provide 1-aza-2-azoniaallene cation inter-
mediates (e.g., 4), which display reactivity reminiscent of
Huisgen-type 1,3-dipolar compounds11 and undergo inter-
molecular [3 þ 2] cycloaddition with alkenes to provide
diazenium salt heterocycles (e.g., 5). We recently reported
the preparation of more structurally complex bicyclic dia-
zenium salts by rendering this Lewis acid-mediated process
intramolecular.12 The success of this intramolecular cycloaddition
(1) Kuznetsov, M. A. Russ. Chem. Rev. 1979, 48, 1054.
(2) Nelsen, S. F.; Landis, R. T. J. Am. Chem. Soc. 1974, 96, 1788.
(3) Nelsen, S. F.; Landis, R. T. J. Am. Chem. Soc. 1973, 95, 2719.
(4) Nelsen, S. F.; Blackstock, S. C. J. Org. Chem. 1984, 49, 1134.
(5) Nelsen, S. F.; Chang, H.; Wolff, J. J.; Powell, D. R. J. Org. Chem.
1994, 59, 6558.
(6) Nelsen, S. F.; Blackstock, S. C.; Frigo, T. B. J. Am. Chem. Soc. 1984,
106, 3366.
(7) Nelsen, S. F.; Blackstock, S. C.; Frigo, T. B. Tetrahedron 1986, 42,
1769.
(8) Wirschun, W. G.; Al-Soud, Y. A.; Nusser, K. A.; Orama, O.; Maier,
G. M.; Jochims, J. C. J. Chem. Soc., Perkin Trans. 1 2000, 4356.
(9) Wang, Q. R.; Amer, A.; Mohr, S.; Ertel, E.; Jochims, J. C. Tetrahedron
1993, 49, 9973.
(10) Al-Soud, Y. A.; Wirschun, W.; Hassan, N. A.; Maier, G. M.;
Jochims, J. C. Synthesis 1998, 721.
(11) Huisgen, R. Angew. Chem., Int. Ed. Engl. 1963, 2, 565.
(12) Javed, M. I.; Wyman, J. M.; Brewer, M. Org. Lett. 2009, 11,
2189.
8078 J. Org. Chem. 2010, 75, 8078–8087
Published on Web 11/10/2010
DOI: 10.1021/jo101706h
r
2010 American Chemical Society

Wyman et al.
JOCArticle
in providing structurally complex heterocyclic products from
simple starting materials encouraged us to explore the formation
of bicyclic diazenium salts further and we present our results here.
We also report our discovery that bicyclic diazenium salts can be
formed directly from hydrazones by reaction with dimethylsulfo-
nium ditriflate.
hypochlorite,21,22 and these products are useful synthetic
precursors to azoalkenes,23 tetrahydropyridazines,23 1,2,4-
triazolium salts,24,25 N-(azoalkyl)iminium salts,26 1,2,4,5-
tetrazinium salts,26 1H-pyrazolium salts,9 diazenium salts,9
and pyrazoles.9
SCHEME 4. Proposed Mechanism of R-Chloroazo Formation
Results and Discussion
Reactions of Hydrazones with Sulfonium Salts. The work
described herein stems from our recent studies on reactions
of hydrazones with sulfonium salts, which we have discovered
can provide a variety of useful products. For example, we have
observed that unsubstituted hydrazones react readily at low
temperature with chlorodimethylsulfonium chloride (Me2SCl2)
in the presence of 2 equiv of triethylamine to provide diazo
products (Scheme 3).13,14 This method of forming diazo
compounds is more environmentally friendly than the well-
established dehydrogenation procedures mediated by lead or
mercury salts,15-18 and it is particularly useful for the forma-
tion of aryl diazomethanes. Unstabilized aliphatic diazo com-
pounds appear to form readily under these reaction conditions,
but these more reactive species are unstable in the presence of the
triethylammonium chloride that is generated over the course of
the reaction.
We hypothesize that Me2SCl2 reacts with hydrazones to
provide R-chloroazo products by the mechanism shown in
Scheme 4. Nucleophilic attack of the hydrazone on the
electrophilic sulfonium salt would provide azasulfonium
salt 10 after deprotonation with Et3N. Lone pair donation
by the R-nitrogen would result in elimination of dimethyl
sulfide to provide the cationic heteroallene 11, which could
in turn be captured by the chloride counterion to provide
R-chloroazo 12a.27
SCHEME 3. Sulfonium Salt-Mediated Formation of Diazos
and Alkyl Chlorides
Lewis Acid-Mediated Diazenium Salt Formation. With a
convenient route to aryl-R-chloroazo alkenes in hand, we
have begun to study the formation of bicyclic diazenium salts
via intramolecular Lewis acid-mediated cycloaddition.12 For
example, treating phenyl-R-chloroazo 12a with antimony
pentachloride resulted in an intramolecular cycloaddition to
provide fused bicyclic diazenium salt 13a as a single diastereo-
mer in 88% isolated yield (entry 1, Table 1). This transformation
efficiently builds structural complexity and over the course of
the reaction new carbocyclic and new heterocyclic rings form.
The diastereoselectivity of this reaction further supports the
notion that the cycloaddition occurs by a concerted process.8
To assess the scope of this intramolecular cycloaddition
reaction we prepared phenyl-R-chloroazo compounds 12a-g
(Table 1) and subjected these to the Lewis acid-mediated
cyclization. Most of these substrates reacted smoothly to pro-
vide the diazenium salt products in good to excellent yield after
purification by trituration from diethyl ether. Of note, electron-
deficient alkene 12c reacted with SbCl5 to provide the desired
diazenium salt 13c (entry 3, Table 1) in 83% yield. This result
is significant because electron-deficient alkenes do not
participate in intermolecular cyclizations of this type8 and
this result broadens the useful substrate range of this
Changing the reaction conditions so that equimolar quan-
tities of triethylamine and hydrazone are used in the reaction
results in the formation of alkyl chloride products rather
than diazo species (Scheme 3).19 This latter transfor-
mation is unique in that the hydrazone starting material
undergoes a net reduction under standard oxidizing
conditions.
Aryl-substituted hydrazones (e.g., 9, Scheme 4), on the other
hand, reacted with Me2SCl2 to provide R-chloroazo products20
(e.g., 12a). This transformation is general and we were pleased
to find that Me2SCl2 smoothly converted hydrazones contain-
ing a pendent alkene into the corresponding R-chloroazo
species with no modification of the olefin. R-Chloroazo
compounds had been prepared previously by reacting sub-
stituted hydrazones with either chlorine gas or tert-butyl
(13) Javed, M. I.; Brewer, M. Org. Lett. 2007, 9, 1789.
(14) Javed, M. I.; Brewer, M. Org. Synth. 2008, 85, 189.
(15) Regitz, M.; Maas, G. Diazo Compounds Properties and Synthesis:
Academic Press, INC.: Orlando, FL, 1986.
(21) Moon, M. W. J. Org. Chem. 1972, 37, 383.
(22) Moon, M. W. J. Org. Chem. 1972, 37, 386.
(16) Heydt, H. In Science of synthesis Houben-Weyl methods of molecular
transformations: Heteroatom Analogues of Aldehydes and Ketones, 5th ed.;
Thieme: Stuttgart, Germany, 2004; Vol. 27, p 843.
(17) Holton, T. L.; Shechter, H. J. Org. Chem. 1995, 60, 4725.
(18) For a summary of other oxidants that effect this conversion but find
less use see ref 16.
(19) Brewer, M. Tetrahedron Lett. 2006, 47, 7731.
(20) Wyman, J. M.; Jochum, S.; Brewer, M. Synth. Commun. 2008, 38,
3623.
(23) Gaonkar, S. L.; Rai, K. M. L. Tetrahedron Lett. 2005, 46, 5969.
(24) Wang, Q. R.; Jochims, J. C.; Kohlbrandt, S.; Dahlenburg, L.;
Altalib, M.; Hamed, A.; Ismail, A. E. H. Synthesis 1992, 710.
(25) Wang, Q. R.; Liu, X. J.; Li, F.; Ding, Z. B.; Tao, F. G. Synth.
Commun. 2002, 32, 1327.
(26) Al-Soud, Y. A.; Shrestha-Dawadi, P. B.; Winkler, M.; Wirschun, W.;
Jochims, J. C. J. Chem. Soc., Perkin Trans. 1 1998, 3759.
(27) Alternatively, the chloride ion could react directly with azasulfonium
0
salt 10 by an SN2 mechanism.
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TABLE 1. Results of Intramolecular Lewis Acid-Mediated Diazenium
Salt Formation
contain adjacent quaternary centers and steric encumbrance
may inhibit cyclization.
Terminal alkene 12e reacted with SbCl5 to provide a
mixture of ring-fused diazenium salt 13e and bridged diaze-
nium salt 14e in a 1 to 0.2 ratio (entry 5, Table 1). Mixtures of
bridged and fused bicyclic diazenium salts were obtained for
other terminal alkenes as well (entries 6 and 7) and the ratio
of these products appears to be affected by steric factors. For
example, Lewis acid-induced cyclization of isopropyl derivative
12f provided a 1 to 0.05 ratio of fused (13f) to bridged (14f)
products, while incorporation of a gem-dimethyl group with-
in the chain (12g) provided the fused (13g) and bridged
(14g) products in a 1 to 0.1 ratio. Formation of the fused
and bridged products can be explained by considering two
alternative orientations by which the alkene can approach the
heteroallene intermediate. These alternate approaches would
lead to transition states 16 and 17 shown in Figure 1, which
would in turn provide the fused and bridged bicyclic prod-
ucts, respectively.
To more fully explore the scope of this transformation
we prepared the 4-chlorophenyl-R-chloroazo compounds
12a0-g0 (Table 1) and subjected these to Lewis acid-mediated
intramolecular cycloaddition as well. Modification of the aryl
substituent from phenyl to 4-chlorophenyl had little effect on
the outcome of this reaction and the corresponding diazenium
salts 13a0,c0,e0-g0 and 14e0-g0 were formed in good to excellent
yield. For reasons we do not fully understand, reactions of
trisubstituted alkene 12b0 consistently provided complex mix-
tures that were intractable and could not be resolved to pure
diazenium salt 13b0. Another notable effect of this modification
was that the terminal alkene substrates 12e0-g0 reacted to
provide bridged and fused products in different ratios than
was observed for the corresponding phenyl derivatives. In
each case, the 4-chlorophenyl substrates provided a modest
increase in the relative proportion of the 6,5-bridged diaze-
nium salt product.
To further assess how the electronics of the aryl ring affect
the outcome of the cycloaddition reaction, we prepared the
aryl-R-chloroazo compounds shown in Table 2 and sub-
jected these compounds to Lewis acid-mediated intramole-
cular cycloaddition. The ratio of the fused to bridged bicyclic
diazenium salt products was determined by proton NMR
analysis of the crude reaction mixtures. From these results,
it is clear that the electronic nature of the aromatic ring
substituent on nitrogen affects the reaction outcome; an
increase in the electron-withdrawing character of the aryl
ring resulted in an increase in the proportion of the 6,5-
bridged bicyclic product that was formed. Conversely, a
more electron-rich aryl ring provided the 5,5-fused product
to an even greater extent (Table 2). A Hammett plot of these
results (Figure 2) shows a linear correlation between the ratio
of the products formed and the Hammett constants for the
aryl ring substituents.28-30
aDiazenium salts 13g’-g/e’-g’ and 14e-g/e’-g’ were isolated as
mixtures. bDiazenium salts 13a and 13c were formed as single diaste-
reomers and their relative configurations were assigned by nOe experi-
ments. cProduct was formed as an intractable mixture. dAfter titration
the only observable product was the minimum tautomer.
transformation. On handling, diazenium salt 13c readily
tautomerized to hydrazonium salt 15. Disubstituted ter-
minal alkene 12d did not provide any of the expected diaze-
nium salt product. In this case, the expected product would
(28) Hammett, L. P. J. Am. Chem. Soc. 1937, 59, 96.
(29) Hammett, L. P. Chem. Rev. 1935, 17, 125.
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FIGURE 1. Proposed transition states leading to diazenium salts
13 and 14.
TABLE 2. Dependence of Product Ratio on the Electronics of Aryl
Substituent
FIGURE 3. Location of charge in the asynchronous cycloaddition
mechanism.
atom that forms a new bond with nitrogen. Transition state
20 (Figure 3), leading to the 6,5-bridged product 14e, would
have a partial positive charge develop on a secondary carbon
atom, whereas proposed transition state 19, leading to the
5,5-fused product 13e, would have a partial positive charge
develop on a primary carbon. While cationic charge buildup
on a primary carbon would make transition state 19 higher in
energy, we suspect that this transition state is entropically
favored, which explains why the fused diazenium salt 13e is
always the dominant species formed (Tables 1 and 2). How-
ever, as the aryl substituent becomes more electron with-
drawing, C-N bond formation should be further delayed
and the amount of partial positive charge developed at the
transition state would increase. If this is the case, then the
amount of bridged diazenium salt (14) formed would be
expected to increase as the aryl ring becomes more electron
withdrawing, which is consistent with our observations
(Table 2). In the case of terminal dimethyl substrate 12b0
(Table 1), a more stepwise process resulting in the formation
of a tertiary carbocation intermediate could explain the
observed formation of complex product mixtures.31
aProduct ratio determined by proton NMR of the crude reaction mixture..
Subjecting R-chloroazo substrate 21 (Scheme 5) to intra-
molecular cyclization could provide either 6,5-fused (22) or
7,5-bridged (23) bicyclic diazenium salts. In this case, for-
mation of the seven-membered carbocyclic ring was favored
over formation of the six-membered ring; the 7,5-bridged
diazenium salt 23 was formed as the major product in a 1 to
0.2 ratio with the 6,5-fused system. This result is important
because methods to prepare carbocyclic 7-membered rings
are generally lacking. As would be expected, changing the
aryl ring to the more electron-withdrawing 4-chlorophenyl
derivative increased the relative proportion of the 7,5-bridged
product (26), and in this case only traces of the 6,5-fused
product were observed.
Preferential formation of the 7,5-bridged products (23 or
26) is likely due to the fact that the reactive orbitals of the
1-aza-2-azoniaallene intermediate (i.e., the heteroallene and
the alkene) cannot productively overlap to form the 6,5-
fused product (22 or 25) when the heteroallene adopts a
conformation in which the 6-membered ring that forms is in
a chairlike conformation (e.g., 27, Figure 4). To obtain
reasonable orbital overlap leading to the 6,5-fused products,
the 1-aza-2-azoniaallene intermediate would need to adopt
an unfavorable conformation in which the 6-membered ring
that forms is in a boat-like conformation (e.g., 28). The longer
tether length seems to provide sufficient flexibility in the
systemto allowthe reacting centers to align ina conformation
FIGURE 2. Hammett plot of log(ratio 14/13) data vs σ for reaction
of 12e, 12e0, 12h0, and 12i0.
The observation that the electronics of the hydrazone aryl
substituent biases the product distribution is consistent with
a concerted but asynchronous mechanism in which C-C
bond formation to the highly electrophilic carbon atom of
heteroallene 18 (Figure 3) is more advanced at the transi-
tion state than N-C bond formation to the heteroallene
nitrogen.10,31 If this is the case, then on route to the transition
state a partial positive charge would build on the carbon
(30) The log of the ratio of products obtained was used for these plots
because (assuming the reaction is irreversible under the reaction conditions)
these values are directly related to the free energy difference between the
regioisomeric transition states. This relationship is analogus to using log(er)
for Hammett plots of results obtained for enantioselective reactions. For an
example of the use of log(er) in Hammett plots see: Constantine, R. N.; Kim,
N.; Bunt, R. C. Org. Lett. 2003, 5, 2279.
(31) Wei, M. J.; Fang, D. C.; Liu, R. Z. J. Org. Chem. 2002, 67, 7432.
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SCHEME 5. Seven-Membered Ring Formation
TABLE 3. Results of Me2S(OTf)2-Mediated Diazenium Salt Formationa
(e.g., 29) leading to the formation of the seven-membered ring
carbocycle without major energetic penalties. In addition, as
discussed above, an asynchronous concerted mechanism
would also favor the formation of 7,5-bridged bicyclic pro-
ducts 23 and 26.
FIGURE 4. Proposed conformations leading to observed products.
Sulfonium Salt-Mediated Conversion of Hydrazones to
Diazenium Salts. The mechanism we propose in Scheme 4
for Me2SCl2-mediated R-chloroazo formation invokes a
1-aza-2-azoniallene salt intermediate (11), which is subse-
quently captured by a chloride counterion. With this in mind,
we hypothesized that a sulfonium salt bearing a non-nucleo-
philic counterion might react with aryl hydrazones to pro-
vide heteroallene intermediates that could then undergo
intramolecular cycloadditions to provide diazenium salt prod-
ucts. In this way, hydrazones would be directly converted into
diazenium salts avoiding the need to prepare and isolate
R-chloroazo compounds as intermediates.
Dimethyl sulfide ditriflate (Me2S(OTf)2) seemed a logical
sulfonium salt to use for this transformation; it is known
to have similar reactivity to Me2SCl2,32 but has a poorly
nucleophilic counterion that we thought unlikely to capture
the heteroallene intermediate. Upon treating hydrazone 30e0
(Table 3, entry 4) with Me2S(OTf)2 and 2,6-di-tert-butyl-4-
methylpyridine (DTBMP), we were pleased to observe that
the expected fused and bridged bicyclic diazenium salts (31e0
and 32e0) were indeed present in the proton NMR spectrum
of the crude reaction mixture, along with small quantities of
what appeared to be an aryldimethyl sulfonium salt presum-
ably formed by electrophilic aromatic substitution.33 In an
effort to optimize this transformation, sulfonium salts de-
rived by activation of dimethyl sulfoxide with acetic anhy-
dride, trifluoroacetic anhydride, or sulfur trioxide/pyridine
complex were tested for their ability to facilitate diazenium
salt formation. Unfortunately, none of these activated DMSO
species provided any of the diazenium salt products. Substi-
tuting pyridine, proton sponge, or 2,6-dichloropyridine as
base in place of DTBMP provided notably less product, and
deprotonating the hydrazone with n-butyllithium prior to
adding Me2S(OTf2) also failed to provide the desired product.
Interestingly, a small amount of diazenium salt formed when
no external base was added; in this case it seems likely that
aConditions: Me2S(OTf)2 (1.1 equiv), 2,6-di-tert-butyl-4-methylpyr-
idine (1.2 equiv) CH2Cl2 (0.02 M), -78 °C (20 min), -78 °C to rt (35-
40 min), added benzyl ether (0.5 equiv), solvent removedin vacuo. bYield
determined by NMR vs an internal standard. cDiazenium salts 31e’-g’
and 32e’-g’ were formed as mixtures. dProduct formed in low yield as an
intractable mixture.
(32) Hendrickson, J. B.; Schwartzman, S. M. Tetrahedron Lett. 1975, 16,
273.
(33) Nenajdenko, V. G.; Vertelezkij, P. V.; Balenkova, E. S. Sulfur Lett.
1996, 20, 75.
another equivalent of hydrazone starting material could be
acting as base to facilitate the transformation.
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To check the reaction time, several reactions were allowed
to proceed at low temperature (-78 °C) for prolonged
periods (up to 48 h). These runs led to inconsistent results;
reaction time did not correlate to reaction outcome, which
indicated to us that reaction temperature might be an im-
portant parameter. To better understand temperature effects
on the course of the reaction we monitored the processes by
variable-temperature NMR. When a -78 °C solution of the
hydrazone and DTBMP in CD2Cl2 was added to a -78 °C
solution of Me2S(OTf2) in CD2Cl2, a significant change in the
proton NMR signals of the hydrazone occurred, indicating
that a reaction had occurred between these two compounds.
However, at this low temperature no diazenium salt product
was observed to form. The temperature of the NMR probe
was raised by 10 °C increments and spectra were recorded at
each stop along the way. Raising the temperature caused no
change in the spectrum until the temperature reached -40 °C,
at which point traces of diazenium salt appeared. Increasing
the temperature to -30 °C provided only slightly more di-
azenium salt. However, a critical temperature was reached
between -30 and -20 °C, and the reaction proceeded to com-
pletion over this temperature range; no changes were noted in
the spectrum above -20 °C. On the basis of these data, we
hypothesize that Me2S(OTf2) reacts rapidly with the hydra-
zone at low temperature to provide an aza-sulfonium inter-
mediate (e.g., 10, Scheme 4) that appears to be stable until
the temperature is increased above -30 °C. At this higher
temperature, formation of the heteroallene and subsequent
intramolecular cycloaddition with the alkene would provide
the diazenium salt products. With these data in mind, it is
not surprising that allowing the -78 °C reaction mixture to
warm to room temperature 20 min after mixing the reagents
consistently provided cleaner products and this became the
procedure of choice.
Lewis acid-mediated cyclization of R-chloroazo 12b0. Hydra-
zone 30c0, bearing a pendant enoate, was also a competent
reactant and after trituration returned iminium ion 31c0 in
44% yield. As noted earlier, iminium ion 31c0 results from
isomerization of the corresponding diazenium salt.
Hydrazones 30e0-g0, each bearing a terminal olefin, all
reacted with Me2S(OTf2) to provide mixtures of fused and
bridged bicyclic diazenium salts in 67%, 66%, and 54%
yield, respectively. In each case, the ratio of bridged to fused
product is comparable to the ratio obtained by the Lewis
acid-mediated cycloaddition, which again supports our sup-
position that these two transformations occur via a common
heteroallene intermediate.
Conclusions
The studies described here indicate that reactions between
hydrazones and sulfonium salts are versatile and useful for
the preparation of a variety of products. Unsubstituted
hydrazones react efficiently at low temperature with Me2-
SOCl2 to provide either alkyl chlorides or diazo compounds
depending on the quantity of base present, whereas aryl-
substituted hydrazones react with Me2SOCl2 to provide
R-chloroazo compounds in good yield. Importantly, when
aryl-substituted hydrazones that contain a pendent alkene are
converted into R-chloroazo compounds the olefin is un-
touched and these products readily participate in Lewis
acid-mediated intramolecular cycloadditions to provide bi-
cyclic diazenium salt products. Our data support the supposi-
tion that this cycloaddition occurs by a concerted8 but
asynchronous mechanism. Aryl hydrazones that bear a pen-
dent alkene could be directly converted into diazenium salt
products by reaction with Me2S(OTf2). These latter transfor-
mations result in the formationof a newcarbon-carbon bond
under mild conditions and provide two new rings: a carbo-
cycle and a cyclic diazenium salt. The reactivity and syn-
thetic utility of cyclic diazenium salts is currently under
investigation and results from these studies will be reported
in due course.
To determine the scope of this one-step diazenium salt-
forming reaction, hydrazones 30a0-g0 were subjected to the
reaction conditions and the results from these studies are
shown in Table 3. The diazenium salt products (31a0-g0
and 32e0-g0) formed in these reactions are highly polar and
labile compounds and our attempts to purify these products
from the reaction mixtures have not yet been fruitful; all
standard purification techniques (e.g., extraction, chroma-
tography, HPLC, ion exchange chromatography) failed to
return clean product. However, the NMR spectra of com-
pounds 13a0-g0 SbCl6 and 14e0-g0 SbCl6 (Table 1) were
Experimental Section
I. Representative Experimental Procedure for the Prepara-
tion of 4-Chlorophenyl Hydrazones:34. 1-(4-Chlorophenyl)-
2-(hept-6-en-2-ylidene)hydrazine (30e0). 4-Chlorophenyl hy-
drazine (0.636 g, 4.46 mmol, 1 equiv) was added to a mixture
3
3
˚
identical to those of the triflate salts shown in Table 3 and
thus identifying the desired products in the product mixtures
was trivial. Yields for these transformations were established
by integration of the NMR spectra by adding a known
quantity of benzyl ether to the reaction mixture to serve as
an internal standard.
of hept-6-en-2-one (0.50 g, 4.46 mmol, 1 equiv) and 4-A molec-
ular sieves in CH2Cl2 (4 mL). After 1.5 h of stirring the
sieves were removed by filtration and the solvent was removed
in vacuo to provide 1-(4-chlorophenyl)-2-(hept-6-en-2-
ylidene)hydrazine (30e0) in 89% yield as a 1:0.17 ratio of
E and Z hydrazone diastereomers. The highly air-sensitive35
product was typically of sufficient purity to use in subsequent
Treating hydrazone 30a0 with Me2S(OTf2) and DTBMP
provided diazenium salt 31a0 in 61% yield. Only a single
diastereomer of 31a0 was observed and the diastereoselectivity
ofthis processisconsistentwiththe selectivityobservedforthe
SbCl5-mediated reaction, which supports the notation that
the Me2S(OTf2)-mediated reaction also proceeds through a
heteroallene intermediate.
Hydrazone 30b0, which has a pendent trisubstituted olefin,
provided diazenium salt 31b0 as a complex mixture in less
than 30% yield. The low yield in this case is not surprising
in view of the poor results obtained for the corresponding
(34) (i) O’Connor, R. J. Org. Chem. 1961, 26, 4375. (ii) Yao, H. C.;
Resnick, P. J. Org. Chem. 1965, 30, 2832. (iii) Harej, M.; Dolenc, D. J. Org.
Chem. 2007, 72, 7214. (iv) Tiecco, M.; Testaferri, L.; Marini, C. S.; Bagnoli,
L.; Temperini, A. Tetrahedron 1997, 53, 7311. (v) The hydrazones could also
be prepared by mixing the ketone, 4-chlorophenyl hydrazine hydrochloride,
and sodium acetate in ethanol under an atmosphere of nitrgen. The mixture
was stirred at room temperature or heated to reflux (for sterically encum-
bered ketones) and the progress of the reaction was monitored by TLC.
Upon completion, the solvent was removed in vacuo to provide the hydra-
zone, which could be further purified by dissolving the residue in pentane and
passing the mixture through a short plug of basic alumina.
(35) Harej, M.; Dolenc, D. J. Org. Chem. 2007, 72, 7214.
J. Org. Chem. Vol. 75, No. 23, 2010 8083

Wyman et al.
JOCArticle
reactions without further purification. Small quantities of
R-azohydroperoxide could be removed by dissolving the
impure hydrazone in pentane and passing the mixture through
a short plug of basic alumina. 1H NMR (500 MHz, CDCl3)
δ 7.17 (d, J = 8.9 Hz, 2H), 6.97 (d, J = 8.9 Hz, 2H), 6.84
(br s, 1H), 5.84 (ddt, J = 16.9, 10.4, 6.8 Hz, 1H), 5.03 (app dq,
J =17.3, 1.6 Hz, 1H), 4.96-4.99 (m, 1H), 2.31 (t, J = 7.5 Hz,
2H), 2.11 (q, J = 7.1 Hz, 2H), 1.85 (s, 3H), 1.68 (p, J = 7.6 Hz,
2H); 13C NMR (125 MHz, CDCl3) δ 147.2, 144.5, 138.4,
128.9, 123.9, 114.8, 114.0, 38.2, 33.3, 25.7, 14.4; MS (ESI)
calcd for [C13H17ClN2H]þ 237.1158, found 237.1158. Obser-
vable resonances for the minor diastereomer: 1H NMR (500
MHz, CDCl3) δ 6.95 (d, J = 8.9 Hz, 2H), 5.06-5.11 (m, 2H),
2.24 (t, J = 8.3 Hz, 2H), 2.01 (s, 3H); 13C NMR (125 MHz,
CDCl3) δ 148.1, 144.4, 137.7, 115.8, 113.9, 28.4, 24.2, 23.1.
II. Characterization Data for 4-Chlorophenyl Hydrazones.
(E)-1-(4-Chlorophenyl)-2-((Z)-oct-6-en-2-ylidene)hydrazine
(30a0). Yield 83%; E/Z 1:0.1; major diastereomer: 1H NMR
(500 MHz, CDCl3) δ 7.17 (d, J = 8.9 Hz, 2H), 6.96 (d, J = 8.7
Hz, 2H), 6.83 (br s, 1H), 5.41-5.44 (m, 1H), 5.33-5.44 (m,
1H), 2.32 (t, J = 7.6 Hz, 2H), 2.04-2.15 (m, 2H), 1.85 (s, 3H),
1.64 (p, J = 7.8 Hz, 2H), 1.60 (d, J = 6.8 Hz, 3H); 13C NMR
(125 MHz, CDCl3) δ 147.4, 144.6, 130.1, 129.0, 124.3, 123.9,
114.1, 38.4, 26.4, 14.4, 12.7; observable resonances for minor
diastereomer: 1H NMR (500 MHz, CDCl3) δ 6.94 (d, J = 8.8
Hz, 2H), 5.53-5.62 (m, 2H), 2.24 (app t, J = 7.5, 2H); 13C
NMR (125 MHz, CDCl3) δ 129.4, 125.6, 123.9, 113.9, 28.6,
26.5, 24.9, 23.1, 12.9; MS (ESI) calcd for [C14H19ClN2H]þ
251.1315, found 251.1313.
(E)-1-(4-Chlorophenyl)-2-(7-methyloct-6-en-2-ylidene)hy-
drazine (30b0). Yield 94%; E/Z 1:0.3; major diastereomer: 1H
NMR (500 MHz, CDCl3) δ 7.17 (d, J = 8.9 Hz, 2H), 6.96 (d,
J = 8.7 Hz, 2H), 5.13 (tp, J = 7.2, 1.5 Hz, 1H), 2.30 (t, J = 7.7
Hz, 2H), 2.00-2.08 (m, 3H), 1.84 (s, 3H), 1.70 (s, 3H), 1.60 (s,
3H), 1.50-1.66 (m, 1H); 13C NMR (125 MHz, CDCl3) δ
147.7, 144.6, 131.9, 129.0, 124.2, 114.1, 38.5, 27.6, 26.7, 25.7,
17.7, 14.4; observable resonances for minor diastereomer: 1H
NMR (500 MHz, CDCl3) δ 6.93 (d, J = 8.7 Hz, 2H),
5.06-5.11 (m, 1H), 2.23 (t, J = 7.4 Hz, 2H), 2.01 (s, 3H);
13C NMR (125 MHz, CDCl3) δ 123.9, 113.9, 17.8; MS (ESI)
calcd for [C15H21ClN2H]þ 265.1472, found 265.1475.
138.8, 114.6, 33.5, 31.0, 26.9, 25.5, 18.8; MS (ESI) calcd for
[C15H21ClN2H]þ 265.1472, found 265.1479.
(E)-1-(4-Chlorophenyl)-2-(4,4-dimethylhept-6-en-2-ylidene)-
hydrazine (30g0). Yield 90%; 1H NMR (500 MHz, CDCl3) δ
7.18 (d, J = 9.2 Hz, 2H), 6.97 (d, J = 9.0 Hz, 2H), 6.87 (br s,
1H), 5.89 (ddt, J = 17.5, 10.2, 7.4 Hz, 1H), 5.00-5.08 (m, 2H),
2.22 (s, 2H), 2.05 (d, J = 7.5 Hz, 2H), 1.89 (s, 3H), 0.96 (s, 6H);
13C NMR (125 MHz, CDCl3) δ 145.4, 144.4, 135.4, 129.0,
123.9, 117.2, 114.0, 50.1, 46.8, 34.5, 27.3, 17.2; observable reso-
nances for minor diastereomer: 1H NMR (500 MHz, CDCl3) δ
6.93 (d, 8.6 Hz, 2H), 5.09-5.17 (m, 2H), 2.18 (s, 3H), 2.09 (d,
6.9 Hz, 2H), 1.03 (s, 6H); MS (ESI) calcd for [C15H21ClN2H]þ
265.1472, found 265.1470.
(E)-1-(Hept-6-en-2-ylidene)-2-(3-nitrophenyl)hydrazine (30h0).
Yield 74%; E/Z 1:0.3; 1H NMR (500 MHz, CDCl3) δ 7.88 (s,
1H), 7.60-7.65 (m, 1H), 7.28-7.37 (m, 2H), 7.14 (br s, 1H), 5.84
(ddt, J = 16.9, 10.3, 6.9 Hz, 1H), 5.02-5.07 (m, 1H), 5.00 (br d,
J =10.1 Hz, 1H), 2.34 (t, J = 7.4Hz, 2H), 2.13(q, J =7.0 Hz,
2H), 1.89 (s, 3H), 1.70 (p, J = 7.4 Hz, 2H); 13C NMR (125
MHz, CDCl3) δ 149.2, 148.9, 146.8, 138.3, 129.7, 118.5, 114.9,
113.9, 107.4, 38.2, 33.3, 25.7, 14.6; observable resonances
for minor diastereomer: 1H NMR (500 MHz, CDCl3) δ 7.10
(s, 1H), 2.27 (t, J = 7.7 Hz, 2H), 2.04 (s, 3H); MS (ESI) calcd
for [C13H17N3O2H]þ 248.1399, found 248.1402.
(E)-1-(Hept-6-en-2-ylidene)-2-(4-methoxyphenyl)hydrazine
(30i0). Yield 92%; E/Z 1:0.2; 1H NMR (500 MHz, CDCl3) δ
7.00 (d, J = 8.9 Hz, 2H), 6.82 (d, J = 8.9, 2H), 6.69 (br s, 1H),
5.84 (ddt, J = 17.0, 10.3, 6.6 Hz, 1H), 4.93-5.06 (m, 2H), 3.76
(s, 3H), 2.30 (t, J = 7.3 Hz, 2H), 2.08-2.16 (m, 2H), 1.84 (s,
3H), 1.68 (p, J = 7.6, 2H); 13C NMR (125 MHz, CDCl3) δ
153.5, 146.4, 140.3, 138.6, 114.7, 114.7, 114.3, 77.3, 77.0, 76.8,
55.7, 38.3, 33.3, 25.9, 14.4; observable resonances for minor
diastereomer: 1H NMR (500 MHz, CDCl3) δ 5.05-5.11 (m,
2H), 2.24 (t, J = 8.0 Hz, 2H), 2.00 (s, 3H); 13C NMR (125
MHz, CDCl3) δ 115.7, 114.2, 28.5, 24.2, 23.1; MS (ESI) calcd
for [C14H20N2OH]þ 233.1654, found 233.1652.
(E)-1-(4-Chlorophenyl)-2-(oct-7-en-2-ylidene). Yield 87%;
E/Z 1:0.2; 1H NMR (500 MHz, CDCl3) δ 7.17 (d, J = 8.9 Hz,
2H), 6.97 (d, J = 8.8 Hz, 2H), 6.83 (br s, 1H), 5.82 (ddt, J =
17.6,10.7, 6.9 Hz, 1H), 4.93-5.04 (m, 2H), 2.30 (t, J = 7.8
Hz, 2H), 2.06-2.13 (m, 2H), 1.84 (s, 3H), 1.56-1.62 (m, 2H),
1.41-1.47 (m, 2H); 13C NMR (125 MHz, CDCl3) δ 147.6,
144.6, 138.8, 129.0, 124.0, 114.5, 114.1, 38.7, 33.6, 28.5, 26.0,
14.4; observableresonances for minor diastereomer:1HNMR
(2E,7E)-Methyl 7-(2-(4-chlorophenyl)hydrazono)oct-2-en-
1
oate (30c0). Yield 84%; major diastereomer: H NMR (500
MHz, CDCl3) δ 7.18 (d, J = 8.7 Hz, 2H), 6.99 (dt, J = 15.6,
7.1 Hz, 1H), 6.97 (d, J = 9.2 Hz, 2H), 6.87 (br s, 1H), 5.85 (dt,
J = 15.6, 1.6 Hz, 1H), 3.73 (s, 3H), 2.33 (t, J = 7.5 Hz, 2H),
2.28 (qd, J = 7.5, 1.6 Hz, 2H), 1.84 (s, 3H), 1.77 (p, J = 7.5
Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 167.0, 149.0, 146.2,
144.4, 128.9, 123.9, 121.3, 114.0, 77.3, 77.0, 76.8, 51.3, 38.0,
31.6, 24.6, 14.5; MS (ESI) calcd for [C15H19ClN2O2H]þ
295.1213, found 295.1209.
(Z)-1-(4-Chlorophenyl)-2-(2-methyloct-7-en-3-ylidene)hydra-
zine (30f0). Yield 92%; E/Z 1:4.7; 1H NMR (500 MHz, CDCl3)
δ 7.17 (d, J = 8.5 Hz, 2H), 6.99 (br s, 1H), 6.96 (d, J = 8.8 Hz,
2H), 5.80-5.95 (ddt, J= 16.6, 10.2, 6.6 Hz, 1H), 5.07-5.12 (m,
2H), 2.53 (sept, J= 6.9 Hz, 1H), 2.2-2.32 (m, 2H), 2.14 (q, J=
7.2 Hz, 2H), 1.62-1.65 (m, 2H), 1.14 (d, J = 6.9 Hz, 6H); 13C
NMR (125 MHz, CDCl3) δ 154.5 144.7, 137.7, 128.9, 123.7,
116.0, 113.9, 35.6, 33.7, 26.2, 24.4, 20.4; observable resonances
for minor diastereomer: 1H NMR (500 MHz, CDCl3) δ 5.01-
5.06 (m, 1H), 4.96-5.00 (m, 1H), 2.87 (sept, J = 6.8 Hz, 1H),
1.11 (d, J= 6.8 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ144.8,
(500 MHz, CDCl3) δ 2.23 (t, J = 7.7 Hz, 2H), 2.01 (s, 3H); 13
C
NMR (125 MHz, CDCl3) δ 32.5, 25.1; MS (ESI) calcd for
[C14H19ClN2H]þ 251.1315, found 251.1317.
III. Representative Experimental Procedure for the Pre-
paration of Aryl-r-chloroazoalkanes:36. 1-(2-Chlorohept-6-en-
2-yl)-2-(4-chlorophenyl)diazene (12e0). Oxalyl chloride (5.15
mmol, 0.44 mL, 1.2 equiv) was added in a dropwise manner
to a stirred solution of DMSO (5.58 mmol, 0.40 mL, 1.3 equiv)
in THF (30 mL) at -55 °C under a nitrogen atmosphere. The
reaction was maintained at -55 °C until gas evolution ceased
(∼20 min) at which point the reaction was cooled further
to -78 °C. A mixture of Et3N (6.43 mmol, 0.90 mL, 1.5 equiv)
and hydrazone 30e0 (1.02 g, 4.29 mmol, 1 equiv) in THF (5 mL)
was added in a dropwise manner via cannula. An immediate
(36) The aryl-R-chloroazoalkane products were moderately stable, but
decomposed on standing. Attempts to send the sample for exact mass
determination failed to provide useful data.
8084 J. Org. Chem. Vol. 75, No. 23, 2010

Wyman et al.
JOCArticle
color change and a concomitant formation of a white pre-
cipitate were noted. The reaction mixture was maintained
at -78 °C for 30 min and was then removed from the cold
bath and warmed to room temperature at which point
the solids were removed by filtration through a medium
porosity sintered-glass funnel. The filtrate was concen-
trated by rotary evaporation and the residue was dissolved
in pentane (∼20 mL) and decanted away from an insoluble
red oil. The pentane was removed in vacuo to provide 1-(2-
chlorohept-6-en-2-yl)-2-(4-chlorophenyl)diazene (12e0) in
80% yield. This material was used in the subsequent step
without further purification. Residual DMSO could be re-
moved by washing the pentane solution with water before
concentrating, but this step was not routinely performed as it
lowered product recovery and was not necessary for the
J = 17.1, 9.79, 7.5 Hz, 1H), 4.96-5.07 (m, 2H), 2.50 (d, J =
15.5 Hz, 1H), 2.30 (d, J = 15.5 Hz, 1H), 1.96-2.1 (m, 2H),
1.91 (s, 3H), 0.95 (s, 3H), 0.92 (s, 3H); 13C NMR (125 MHz,
CDCl3) δ 149.2, 137.4, 135.0, 129.4, 124.3, 117.6, 96.6, 53.7,
48.5, 34.8, 31.6, 28.5, 28.4.
1-(2-Chlorohept-6-en-2-yl)-2-(3-nitrophenyl)diazene (12h0).
Yield 75%; 1H NMR (500 MHz, CDCl3) δ 8.57 (s, 1H), 8.34
(d, J = 8.2 Hz, 1H), 8.14 (d, J = 8.2 Hz, 1H), 7.70 (t, J = 8.2
HZ, 1H), 5.80 (ddt, J = 17.0, 10.2, 6.9 Hz, 1H), 4.95-5.06 m
(2H), 2.31 (ddd, J = 14.1, 11.8, 4.7 Hz, 1H), 2.21 (ddd, J =
14.4, 11.9, 4.6 Hz, 1H), 2.09 (q, J = 6.9 Hz, 2H), 1.93 (s, 3H),
1.59-1.71 (m, 1H), 1.44-1.55 (m, 1H); 13C NMR (125 MHz,
CDCl3) δ 151.3, 148.9, 137.8, 130.1, 129.4, 125.4, 117.0,
115.2, 96.5, 42.0, 33.3, 28.7, 23.4.
1-(2-Chlorohept-6-en-2-yl)-2-(4-methoxyphenyl)diazene (12i0).
Yield 82%; 1H NMR (500 MHz, CDCl3) δ 7.77 (d, J = 8.8 Hz,
2H), 6.97 (d, J = 8.8 Hz, 2H), 5.78 (ddt, J = 17.1, 10.2, 6.7 Hz,
1H), 5.01 (app d, J = 17.2 Hz, 1H), 4.93-4.98 (app d, J = 10.4
Hz, 1H), 3.87 (s, 3H), 2.27 (ddd, J= 14.2, 12.0, 4.7 Hz, 1H), 2.16
(ddd, J = 14.1, 11.9, 4.7 Hz, 1H), 2.09 (q, J = 7.0 Hz, 2H), 1.88
(s, 3H), 1.58-1.70 (m, 1H), 1.46-1.57 (m, 1H); 13C NMR (125
MHz, CDCl3) δ 162.2, 145.1, 138.2, 124.9, 115.0, 114.1, 96.5,
55.6, 42.4, 33.5, 28.8, 23.5.
1
subsequent transformation. H NMR (500 MHz, CDCl3) δ
7.75 (dm, J = 8.6, 1.9 Hz, 2H), 7.48 (dm, J = 8.6, 1.9 Hz, 2H),
5.78 (ddt, J = 16.9, 10.2, 6.6 Hz, 1H), 5.01 (app dq, J = 17.0,
1.6 Hz, 1H), 4.95-4.98 (m, 1H), 2.28 (ddd, J = 14.0, 12.0, 4.7
Hz, 1H), 2.17 (ddd, J = 14.0, 12.0, 4.6 Hz, 1H), 2.09 (q, J =
7.3 Hz, 2H), 1.89 (s, 3H), 1.60-1.70 (m, 1H), 1.44-1.53 (m,
1H); 13C NMR (125 MHz, CDCl3) δ 149.3, 138.0, 137.3,
129.3, 124.2, 115.1, 96.5, 42.2, 33.4, 28.7, 23.4.
IV. Characterization Data for 4-Chlorophenyl-r-chloroazo
Alkanes. (E)-1-((Z)-2-Chlorooct-6-en-2-yl)-2-(4-chlorophenyl)-
diazene (12a0). Yield 83%; 1H NMR (500 MHz, CDCl3) δ 7.72
(d, J = 8.6 Hz, 2H), 7.45 (d, J = 8.6 Hz, 2H), 5.44-5.50 (m,
1H), 5.32-5.38 (m, 1H), 2.28 (ddd, J = 14.1, 11.9, 4.7 Hz, 1H),
2.17 (ddd, J = 14.1, 11.9, 4.7 Hz, 1H), 2.08 (q, J = 7.3 Hz, 2H),
1.89 (s, 3H), 1.54-1.68 (m, 1H), 1.59 (d, J= 6.7 Hz, 3H), 1.41-
1.50 (m, 1H); 13C NMR (125 MHz, CDCl3) δ 149.3, 137.3,
129.7, 129.3, 124.6, 124.2, 96.5, 42.3, 28.7, 26.5, 24.1, 12.8.
1-(2-Chloro-7-methyloct-6-en-2-yl)-2-(4-chlorophenyl)diazene
(12b0). Yield 87%; 1H NMR (500 MHz, CDCl3) δ 7.71 (d, J =
8.6 Hz, 2H), 7.45 (d, J = 8.6 Hz, 2H), 5.08 (t, J = 7.1 Hz, 1H),
2.25 (ddd, J= 14.0, 11.8, 4.5 Hz, 1H), 2.16 (ddd, J= 14.0, 11.8,
4.6 Hz, 1H), 2.01 (q, J = 7.3 Hz, 2H), 1.89 (s, 3H), 1.68 (s, 3H),
1.58 (s, 3H), 1.55-1.65 (m, 1H), 1.40-1.47 (m, 1H); 13C NMR
(125 MHz, CDCl3) δ 149.3, 137.2, 132.0, 129.2, 124.2, 123.8,
96.5, 42.4, 28.6, 27.7, 25.6, 24.4, 17.7.
(E)-Methyl 7-Chloro-7-((E)-(4-chlorophenyl)diazenyl)oct-
2-enoate (12c0). Yield 69%; 1H NMR (500 MHz, CDCl3) δ
7.72 (d, J = 8.6 Hz, 2H), 7.45 (d, J = 8.6 Hz, 2H), 6.94 (dt,
J = 15.7, 7.0, Hz, 1H), 5.83 (dt, J = 15.7, 1.5 Hz, 1H), 3.72 (s,
3H), 2.30 (ddd, J = 14.0, 11.8, 4.6 Hz, 1H), 2.25 (qd, J = 7.3,
1.4 Hz, 2H), 2.18 (ddd, J = 14.1, 12.9, 4.6 Hz), 1.89 (s,
3H),1.68-1.78 (m, 2H), 1.51-1.63 (m, 2H); 13C NMR (125
MHz, CDCl3) δ 167.3, 149.6, 148.6, 137.8, 129.7, 124.6,
121.9, 96.4, 51.8, 42.9, 42.5, 32.1, 31.7, 30.3, 29.1, 23.0, 22.2.
1-(3-Chloro-2-methyloct-7-en-3-yl)-2-(4-chlorophenyl)diazene
(12f0). Yield 95%; 1H NMR (500 MHz, CDCl3) δ 7.71 (d, J =
8.6 Hz, 2H), 7.45 (d, J = 8.6 Hz, 2H), 5.74 (ddt, J = 16.9, 10.2,
6.7 Hz, 1H), 4.95 (app dq, J = 17.1, 1.7 Hz, 1H), 4.92-4.96 (m,
1H), 2.65 (septet, J = 6.71 Hz, 1H), 2.37 (ddd, J = 14.1, 11.8,
4.6 Hz, 1H), 2.20 (ddd, J = 14.0, 12.0, 4.4 Hz, 1H), 2.05 (q, J =
7.2 Hz, 2H), 1.55-1.64 (m, 1H), 1.21-1.30 (m, 1H), 1.15 (d,
J= 6.8 Hz, 3H), 0.94 (d, J=6.8Hz, 3H);13C NMR (125 MHz,
CDCl3) δ 149.3, 138.0, 137.1, 129.3, 124.1, 115.0, 104.2, 39.3,
37.7, 33.5, 22.9, 17.5, 17.4.
(E)-1-(2-Chlorooct-7-en-2-yl)-2-(4-chlorophenyl)diazene (24).
Yield 60%; 1H NMR (500 MHz, CDCl3) δ 7.71 (d, J = 8.7 Hz,
2H), 7.45 (d, J = 8.6 Hz, 2H), 5.78 (ddt, J = 16.9, 10.1, 6.8 Hz,
1H), 4.90-5.04 (m, 2H), 2.24-2.32 (m, 1H), 2.13-2.20 (m,
1H), 2.01-2.10 (m, 2H), 1.89 (s, 3H), 1.51-1.59 (m, 1H), 1.37-
1.46 (m, 3H); 13C NMR (125 MHz, CDCl3) δ 149.7, 138.8,
137.7, 129.7, 124.6, 115.0, 96.9, 43.0, 33.8, 29.1, 29.0, 24.0.
V. Representative Experimental Procedures for the Formation
of Bicyclic Diazenium Salts. Method A: Lewis acid-mediated
formation of bicyclic diazenium salts from R-chloroazo
compounds:
6a-Methyl-2-(4-chlorophenyl)-3,3a,4,5,6,6a-hexahydrocyclo-
penta[c]pyrazol-2-ium Hexachlorostibate(V) (13e0). Antimony
pentachloride (3.56 mmol, 0.455 mL, 1 equiv) was added drop-
wise to a stirred solution of the R-chloroazoalkane 12e0 (3.56
mmol, 0.965 g, 1 equiv) in CH2Cl2 (40 mL) at -60 °C under a
nitrogen atmosphere. The cooling bath was allowed to warm
slowly to 0 °C (∼45 min) and the reaction was maintained
at that temperature for 1 h. The mixture was allowed to stir
at room temperature for 10 min at which point the solvent
was removed in vacuo to provide a dark oil or foam. This crude
material was analyzed by proton NMR (CD3CN) to determine
the ratio of fused to bridged diazenium salt products. The NMR
sample was recombined with the crude reaction mixture, the
solvent was removed in vacuo, and the residue was triturated
with Et2O to provide the desired diazenium salt as a powder in
92% yield: 1H NMR (500 MHz, CD3CN) δ 8.09 (d, J = 9.1 Hz,
2H), 7.76 (d, J = 9.3 Hz, 2H), 5.54 (dd, J = 17.2, 9.2 Hz, 1H),
5.13 (dd, J = 17.2, 4.5 Hz, 1H), 2.92-2.97 (m, 1H), 2.45-2.54
(m, 1H), 2.03-2.17 (m, 2H), 1.80 (s, 3H), 1.72-1.82 (m, 2H),
1.45-1.56(m,1H);13C NMR (125 MHz, CDCl3) δ143.8, 139.1,
131.7, 126.7, 101.2, 78.0, 43.2, 39.8, 33.7, 25.1, 23.8; observable
resonances for minor isomer: 6-(4-chlorophenyl)-1-methyl-6,7-
diazabicyclo[3.2.1]oct-6-en-6-ium hexachlorostibate(V) (14e0):1H
NMR (500 MHz, CD3CN) δ 8.09 (d, J = 6.6 Hz, 2H), 7.79 (d,
J = 6.1 Hz, 2H), 6.05 (app t, J = 5.1 Hz, 1 H), 1.87 (s, 3H); 13C
NMR (125 MHz, CD3CN) δ 144.6, 132.3, 87.5, 83.7, 29.4, 22.9,
22.6, 18.4; IR (ATR, cm-1) 1586, 1529, 1413, 1095, 831; MS (ESI)
calcd for [C13H16ClN2]þ 235.1002, found 235.0998.
1-(2-Chloro-4,4-dimethylhept-6-en-2-yl)-2-(4-chlorophenyl)-
diazene (12g0). Yield 86%; 1H NMR (500 MHz, CDCl3)
δ 7.75 (d, J = 8.6 Hz, 2H), 7.48 (d, J = 8.6 Hz, 2H), 5.81 (ddt,
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Wyman et al.
JOCArticle
Method B: Dimethyl sulfide ditriflate mediated formation
of bicyclic diazenium salts from hydrazones:
IR (ATR, cm-1) 1530, 1414, 1092, 828; MS (ESI) calcd for
[C15H20ClN2]þ 263.1315, found 263.1319.
6a-Methyl-2-(4-chlorophenyl)-3,3a,4,5,6,6a-hexahydrocyc-
lopenta[c]pyrazol-2-ium Triflate (31e0). Trifilic anhydride (0.82
mmol, 0.14 mL, 1.1 equiv) was added dropwise to a -78 °C
solution of DMSO (0.86 mmol, 0.06 mL, 1.15 equiv) in CH2Cl2
(32 mL). After 20 min a solution of 4-chlorophenyl hydrazone
(0.75 mmol, 0.18 g, 1 equiv) and 2,6-di-tert-butyl-4-methylpyri-
dine (0.89 mmol, 0.18 g, 1.2 equiv) in CH2Cl2 (5 mL) was added.
The resulting bright yellow solution was stirred for 20 min
during which time a fine precipitate often formed. The dry
ice dewar was removed and the solution was allowed to
warm to room temperature over 30 min during which time
the silky precipitate dissolved and an orange solution re-
sulted. Upon warming to room temperature, a known
quantity of dibenzyl ether (0.37 mmol, 0.07 mL, 0.5 equiv)
was added to the reaction mixture as an internal NMR
standard and the solvent was removed in vacuo at 60 Torr to
provide an orange powder. The ratio of diazenium salt to
dibenzyl ether was determined by proton NMR analysis
(CD3CN), which showed the desired product had formed in
67% yield. Spectroscopic data matched that of hexachlor-
ostibate salts 13e0 and 14e0.
VI. Characterization Data for the Diazenium Salt Products. 2-
(4-Chlorophenyl)-3,6a-dimethyl-3,3a,4,5,6,6a-hexahydrocyclop-
enta[c]pyrazol-2-ium Hexachlorostibate(V) (13a0) or Triflate
(31a0). Method A yield 87%; Method B yield 61%; 1H NMR
(500 mHz, CD3CN) δ 7.95 (d, J = 9.1 Hz, 2H), 7.76 (d, J = 9.1
Hz, 2H), 5.94 (dq, J = 9.3, 7.2 Hz, 1H), 2.96-3.00 (m, 1H),
2.45-2.53 (m, 1H), 2.18-2.25 (m, 1H), 1.76-1.92 (m, 3H),
1.79 (s, 3H), 1.58 (d, J = 7.2 Hz, 3H), 1.42-1.53 (m, 1H); 13C
NMR (125 MHz, CD3CN) δ 142.8, 138.1, 131.5, 127.3, 99.8,
84.6, 46.9, 39.7, 28.6, 25.6, 24.1, 15.7; IR (ATR, cm-1) 1518,
1441, 1409, 1095, 832; MS (ESI) calcd for [C14H18ClN2]þ
249.1158, found 249.1153.
5,5,6a-Trimethyl-2-(4-chlorophenyl)-3,3a,4,5,6,6a-hexahy-
drocyclopenta[c]pyrazol-2-ium Hexachlorostibate(V) (13g0) or
Triflate (31g0). Method A yield 89%; Method B yield 54%; 1H
NMR (500 MHz, CD3CN) δ 8.11 (d, J = 9.1 Hz, 2H), 7.76
(d, J=9.3 Hz, 2H), 5.41 (dd, J=16.2, 7.9 Hz, 1H), 5.23 (dd,
J =16.2, 2.3 Hz, 1H), 3.12 (qd, J = 8.0, 2.3 Hz, 1H), 2.26 (d,
J=13.9 Hz, 1H), 2.20(dd, J=14.3, 1.7 Hz, 1H), 2.05 (ddd, J =
13.1, 8.3, 1.6 Hz, 1H), 1.75(s, 3H), 1.47 (ddd, J = 13.1, 9.3, 1.6
Hz, 1H), 1.13 (s, 3H), 1.02 (s, 3H); 13C NMR (125 MHz,
CD3CN) δ 143.9, 139.2, 131.8, 127.0, 101.0, 77.0, 51.2, 47.6,
43.2, 39.8, 28.5, 28.3, 25.0; observable resonances for minor iso-
mer: 6-(4-chlorophenyl)-1,3,3-trimethyl-6,7-diazabicyclo[3.2.1]-
oct-6-en-6-ium hexachlorostibate(V) (14g0) or triflate (32g0): 1H
NMR (500 MHz, CD3CN) δ 8.18 (d, J = 9.1 Hz, 2H), 7.82 (d,
J = 9.3 Hz, 2H), 5.94-5.96 (m, 1H), 1.89 (s, 3H); 13C NMR
(125 MHz, CD3CN) δ 132.7, 126.7, 87.6, 81.7, 43.0, 36.4, 31.7,
23.2; IR (ATR, cm-1) 1524, 1412, 1094, 831; MS (ESI) calcd
for [C15H20ClN2]þ 263.1315, found 263.1312.
6a-Methyl-2-(3-nitrophenyl)-3,3a,4,5,6,6a-hexahydrocycl-
openta[c]pyrazol-2-ium Hexachlorostibate(V) (13h0). Method
A yield 81%; proton NMR resonances assignable to 13h0: 1H
NMR (500 MHz, CD3CN) δ 8.87 (t, J = 2.1 Hz, 1H), 8.68
(dd, J = 8.3, 1.7 Hz, 1H), 8.46 (dd, J = 8.3, 2.2 Hz, 1H), 8.01
(t, J = 8.3 Hz, 1H), 5.61 (dd, J = 17.3, 9.7 Hz, 1H), 5.23 (dd,
J = 17.3, 4.2 Hz, 1H), 2.97-3.05 (m, 1H), 1.86 (s, 3H); proton
NMR resonances assignable to 1-methyl-6-(3-nitrophenyl)-
6,7-diazabicyclo[3.2.1]oct-6-en-6-ium hexachlorostibate-
(V) (14h0): 1H NMR (500 MHz, CD3CN) δ 8.93 (t, J = 2.1
Hz, 1H), 8.71 (dd, J = 8.3, 1.7 Hz, 1H), 8.54 (dd, J = 8.3, 2.4
Hz, 1H), 8.04 (t, J = 8.4 Hz, 1H), 6.17 (t, J = 5.2 Hz, 1H), 2.38
(d, J = 11.8 Hz, 1H), 1.93 (s, 3H), 0.92-1.04 (m, 1H); proton
NMR resonances assignable to 13h0 and 14h0: 2.52-2.62 (m,
2H), 1.74-2.22 (m, 10 H); carbon NMR resonances assignable
to13h0 and 14h0:13C NMR (125 MHz, CD3CN) δ 150.1, 149.6,
140.6, 139.2, 133.3, 132.8, 131.8, 131.2, 130.5, 130.4, 120.2,
120.1, 101.7, 88.5, 84.5, 78.5, 43.1, 43.0, 39.7, 33.4, 29.1, 24.7,
23.6, 22.6, 22.0, 18.0; IR (ATR, cm-1) 1529, 1454, 1349, 803,
735; MS (ESI) calcd for [C13H16N3O2]þ 246.1243, found
246.1248.
6a-Methyl-2-(4-methoxyphenyl)-3,3a,4,5,6,6a-hexahydro-
cyclopenta[c]pyrazol-2-ium Hexachlorostibate(V) (13i0). Method
A yield 92%; 1H NMR (500 MHz, CD3CN) δ 8.09 (d, J = 8.9
Hz, 2H), 7.20 (d, J = 8.9 Hz, 2H), 5.47 (dd, J = 16.7, 9.7 Hz,
1H), 5.07 (dd, J = 16.7, 4.1 Hz, 1H), 3.97 (s, 3H), 2.86-2.93
(m, 1H), 2.41-2.47 (m, 1H), 2.03-2.08 (m, 2H), 1.76 (s, 3H),
1.98-2.03 (m, 1H), 1.41-1.54 (m, 2H); 13C NMR (125 MHz,
CDCl3) δ 166.1, 132.2, 126.6 (br), 115.5, 98.1, 75.8, 56.1, 41.8,
38.4, 32.4, 23.7, 22.5; IR (ATR, cm-1) 1580, 1513, 1429, 1246,
1171, 1097, 1021, 835; MS (ESI) calcd for [C14H19N2O]þ
231.1497, found 231.1498.
7-(4-Chlorophenyl)-1-methyl-7,8-diazabicyclo[4.2.1]non-7-
en-7-ium Hexachlorostibate(V) (26). Method Ayield62%;1H
NMR (500 MHz, CD3CN) δ 8.14 (d, J = 8.9 Hz, 2H), 7.79 (d,
J = 8.9 Hz, 2H), 6.08-6.10 (m, 1H), 2.67 (d, J = 13.3 Hz,
1H), 2.36-2.41 (m, 2H), 2.02-2.21 (m, 3H), 1.86 (s, 3H),
1.68-1.77 (m, 2H), 1.24-1.32 (m, 2H); 13C NMR (125 MHz,
CDCl3) δ 144.0, 137.2, 132.2, 126.9 (br), 90.7,85.2, 41.2,
35.6, 33.5, 25.7, 24.6, 23.9; IR (ATR, cm-1) 1519, 1411,
1094, 829; MS (ESI) calcd for [C14H18ClN2]þ 249.1158, found
249.1153.
2-(4-Chlorophenyl)-3-(methoxycarbonyl)-6a-methyl-1,3a,4,5,
6,6a-hexahydrocyclopenta[c]pyrazol-2-ium Hexachlorostibate-
(V) (13c0) or Triflate (31c0). Method A yield 69%; Method B
1
yield 44%; H NMR (500 MHz, CD3CN) δ 8.07 (s, 1H),
7.60-7.66 (m, 4H), 3.93 (dd, J = 9.8, 5.0 Hz, 1H), 3.79 (s,
3H), 2.27-2.37 (m, 2H), 2.09-2.18 (m, 1H), 1.76-1.88 (m,
3H), 1.57 (s, 3H); 13C NMR (125 MHz, CD3CN) δ 157.2,
151.0, 139.7, 134.5, 130.78, 127.5, 73.8, 58.8, 55.0, 42.9, 34.2,
26.0, 25.9; IR (ATR, cm-1) 1746, 1515, 1436, 1096, 838, 829;
MS (ESI) calcd for [C15H18O2ClN2]þ 293.1057, found
293.1056.
6a-Isopropyl-2-(4-chlorophenyl)-3,3a,4,5,6,6a-hexahydrocy-
clopenta[c]pyrazol-2-ium Hexachlorostibate(V) (13f0) or Tri-
flate (31f0). Method A yield 80%; Method B yield 66%; 1H
NMR (500 MHz, CD3CN) δ 8.12 (d, J = 9.2 Hz, 2H), 7.76
(d, J = 9.2 Hz, 2H), 5.53 (dd, J = 17.5, 9.8 Hz, 1H), 5.14 (dd,
J = 17.5, 4.4 Hz, 1H), 3.11-3.16 (m, 1H), 2.43 (septet, J =
6.5 Hz, 1H), 2.37-2.40 (m, 1H), 2.23-2.29 (m, 1H), 1.90-
1.98 (m, 1H), 1.74-1.81 (m, 2H), 1.41-1.50 (m, 1H), 1.16 (d,
J = 6.9 Hz, 3H), 1.12 (d, J = 6.3 Hz, 3H); 13C NMR (125
MHz, CD3CN) δ 144.0, 139.0, 131.8 (t), 127.0 (m), 108.7,
78.0, 40.1, 37.2, 35.4, 33.8, 24.6, 18.6, 18.3; observable reso-
nances for minor isomer: 6-(4-chlorophenyl)-1-isopropyl-6,7-
diazabicyclo[3.2.1]oct-6-en-6-ium hexachlorostibate(V) (14f0)
or triflate (32f0): 1H NMR (500 MHz, CD3CN) δ 8.19 (d, J =
9.3 Hz, 2H), 7.79 (d, J = 9.3 Hz, 2H), 6.04-6.10 (m, 1H); 13C
NMR (125 MHz, CD3CN) δ 38.8, 34.5, 25.4, 22.9, 18.4, 17.9;
8086 J. Org. Chem. Vol. 75, No. 23, 2010

Wyman et al.
JOCArticle
Acknowledgment. We thank Dr. John Greaves (University
of California, Irvine) for obtaining mass spectral data, and
Dr. Bruce Deker (University of Vermont) for assistance with
NMR characterization. We thank Prof. Mary P. Watson
(Univeristy of Delaware) for helpful discussions related to
the Hammett correlations. This material is based upon
work supported by the National Science Foundation under
CHE-0748058 and instrumentation grant CHE-0821501.
Financial support fromtheUniversityofVermontisgratefully
acknowledged. M.B. thanks Amgen for financial support in
the form of a new faculty award.
Supporting Information Available: General experimental
details and copies of 1H and 13C NMR spectra for compounds
12a0-c0, 12e0-i0, 13a0, 13c0, 13e0-i0, 14e0-h0, 24, 26, 30a0-c0,
30e0-i0, 31a0, 31c0, 31e0-g0, 32e0-g0. This material is available
free of charge via the Internet at http://pubs.acs.org.
J. Org. Chem. Vol. 75, No. 23, 2010 8087