Rearrangements of 4-Quinolylcarbene, 3-Quinolylcarbene, and 2-Quinolylcarbene to 1-Naphthylnitrene and Cyanoindenes by Falling Solid Flash Vacuum Pyrolysis

Article abstract of DOI:10.1021/acs.joc.6b00444

The relationship between 4-quinolylcarbene 17, 3-quinolylcarbene 21, 2-quinolylcarbene 25, and 1-naphthylnitrene 35 has been explored experimentally and computationally. The diazomethylquinolines generated from (5-tetrazolyl)quinolines or 1,2,3-triazolo[1,5-a]quinoline by conventional flash vacuum pyrolysis (FVP) were observed by IR spectroscopy. The carbenes were generated by falling solid flash vacuum pyrolysis (FS-FVP). 4-Quinolylcarbene 17 was found to rearrange to 3-quinolylcarbene 21 and then to 2-quinolylcarbene 25, and finally via 1-naphthylnitrene 35 to 1-cyanoindene 36, which then isomerizes to 3- and 2-cyanoindenes 12 and 13. The thermal rearrangement of 2-quinolylcarbene to 1-naphthylnitrene was verified by ESR spectroscopy. The reaction mechanism has been elucidated with the help of calculations of the structures and energies of the quinolylcarbenes and 1-naphthylnitrene and the intervening aza-benzobicyclo[4.1.0]heptatrienes, aza-benzocycloheptatetraenes, and aza-benzocycloheptatrienylidenes and the transition states connecting them at the B3LYP/6-31G? level. The nonobserved 1,2-hydrogen shifts in aza-benzocycloheptatetraenes/aza-benzocycloheptatrienylidenes are found to have very high activation barriers.

Full text of DOI:10.1021/acs.joc.6b00444

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Article
Rearrangements of 4-Quinolylcarbene, 3-Quinolylcarbene
and 2-Quinolylcarbene to 1-Naphthylnitrene and
Cyanoindenes. Falling Solid Flash Vacuum Pyrolysis
Nigel Aylward, David Kvaskoff, Jürgen Becker, and Curt Wentrup
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b00444 • Publication Date (Web): 06 May 2016
Downloaded from http://pubs.acs.org on May 11, 2016
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Rearrangements of 4-Quinolylcarbene, 3-Quinolylcarbene and
2
-Quinolylcarbene to 1-Naphthylnitrene and Cyanoindenes. Falling Solid
Flash Vacuum Pyrolysis
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,
†
†
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‡
Nigel Aylward, David Kvaskoff, Jürgen Becker, and Curt Wentrup*
†School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Qld
072Australia. Email: wentrup@uq.edu.au
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‡Fachbereich Chemie der PhilippsꢀUniversität, Dꢀ35037 Marburg, Germany.
CH
17,21N
N
CH
25
N
CN
35
36
Abstract: The relationship between 4ꢀquinolylcarbene 17, 3ꢀquinolylcarbene 21, 2ꢀ
quinolylcarbene 25, and 1ꢀnaphthylnitrene 35 has been explored experimentally and
computationally. The diazomethylquinolines generated from (5ꢀtetrazolyl)quinolines or 1,2,3ꢀ
triazolo[1,5ꢀa]quinoline by conventional flash vacuum pyrolysis (FVP) were observed by IR
spectroscopy. The carbenes were generated by falling solid flash vacuum pyrolysis (FSꢀFVP). 4ꢀ
Quinolylcarbene 17 was found to rearrange to 3ꢀquinolylcarbene 21 and then to 2ꢀ
quinolylcarbene 25, and finally via 1ꢀnaphthylnitrene 35 to 1ꢀcyanoindene 36, which then
isomerizes to 3ꢀ and 2ꢀcyanoindenes 12 and 13. The thermal rearrangement of 2ꢀquinolylcarbene
to 1ꢀnaphthylnitrene was verified by ESR spectroscopy. The reaction mechanism has been
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elucidated with the help of calculations of the structures and energies of the quinolylcarbenes and
1ꢀnaphthylnitrene
and
the
intervening
azaꢀbenzobicyclo[4.1.0]heptatrienes,
azaꢀ
benzocycloheptatetraenes and azaꢀbenzocycloheptatrienylidenes and the transition states
connecting them at the B3LYP/6ꢀ31G* level. The nonꢀobserved 1,2ꢀhydrogen shifts in azaꢀ
benzocycloheptatetraenes/azaꢀbenzocycloheptatrienylidenes are found to have very high
activation barriers.
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Introduction
The matrix photochemistry of several hetarylcarbenes and the isomeric (het)arylnitrenes has
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been reviewed recently, and it has been established that nitrenes are generally
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thermodynamically more stable than the isosteric carbenes. The rearrangement of 4ꢀ
pyridylcarbene 1 to 3ꢀpyridylcarbene 3 to 2ꢀpyridylcarbene 6 and finally to phenylnitrene 8 has
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,4, 5,6
been investigated in great detail (Scheme 1).
Scheme 1. The Rearrangement of the Pyridylcarbenes 1, 3, and 6 to Phenylnitrene 8
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Recent C labeling studies have allowed the mechanisms of the ring contraction of
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phenylnitrene to cyanocyclopentadiene, and of 1ꢀisoquinolylcarbene 9 to 3ꢀ and 2ꢀcyanoindenes
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2 and 13 (Scheme 2) to be elucidated.
Scheme 2. Ring contraction of 1-Isoquinolylcarbene to Cyanoindenes 12 and 13. Two
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Routes (a) and (b) Yield Different C-Labeling Outcomes
Here we report the thermal rearrangements of the isomeric quinolylcarbenes 17, 21, and
2
5 to 1ꢀnaphthylnitrene 35 and cyanoindenes 12 and 13.
Results and Discussion
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The tetrazoles 14, 18 and 22 were used as precursors for 4ꢀquinolylcarbene 17, 3ꢀ
quinolylcarbene 21, and 2ꢀquinolylcarbene 25, respectively (Scheme 3). 5ꢀSubstituted tetrazoles
ꢀ
+
can elminate N from the 2Hꢀtautomer to yield nitrile imines RC( )N( )NH, but at high
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temperatures under FVP conditions the formation of diazo compounds and thence carbenes is
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preferred, probably because the 5Hꢀtautomers of the tetrazoles are populated. This reaction
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makes tetrazoles convenient precursors of carbenes in FVP reactions. However, 5ꢀsubstituted
tetrazoles can also undergo a cycloreversion process to HN and a nitrile, which are therefore
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very common byꢀproducts. In the present case, nitriles 15, 19, and 23 are invariably obtained as
byꢀproducts in 50ꢀ60% yields.
Scheme 3. Generation of Quinolylcarbenes by FVP or FS-FVP
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o
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When tetrazole 14 was pyrolyzed at 320 C/10 hPa with deposition of the product on a
KBr window cooled with liquid N , the diazomethane intermediate 16 was detected by an
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ꢀ1
absorption at 2070 cm in the IR spectrum of the solid film. Similarly, the diazomethanes 20 and
ꢀ1
24D were detectable by absorptions at 2070 cm following mild pyrolyses of tetrazoles 18 and
o
2
2 at 400 C (see Scheme 3 and Figure S1a, Supporting Information). Compound 24D has been
ꢀ1
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generated photochemically and absorbs at 2089 cm in an Ar matrix. 1,2,3ꢀTriazolo[1,5ꢀ
a]quinoline 24T is the stable form of diazo compound 24D, and the two are thermally
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o
interconvertible. The intensity of the diazo absorption of 24D increased at 500 and 620 C
under conditions where 2ꢀquinolylcarbene 25 is already being formed with consequential
rearrangement to 2ꢀ and 3ꢀcyanoindenes (see Figure S1bꢀc, Supporting Information). The diazo
o
absorption disappeared on warming the cold pyrolyzate above ꢀ35 C, and it was not observable
o
following FVP at temperatures below 400 C.
Because the tetrazoles have low vapour pressures, conventional FVP is slow and gives
poor yields under preparative conditions. Therefore, we used the falling solid flash vacuum
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o
ꢀ3
ꢀ1
pyrolysis (FSꢀFVP). Using this technique, tetrazole 14 was pyrolyzed at 650 C/10 ꢀ10 hPa
to yield a ca. 3:1 mixture of 3ꢀ and 2ꢀcyanoindenes 12 and 13 (36%) together with 4ꢀ
quinolinecarbonitrile 15 (61%) (see Schemes 3 and 4). Analogous pyrolyses of tetrazole 18
afforded analogous products, viz. a 3:1 mixture of 3ꢀ and 2ꢀcyanoindenes 12 and 13 (40%) as
well as 3ꢀquinolinecarbonitrile 19 (57%). 3ꢀQuinolylcarbene 21 has been generated previously
1
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by photolysis of the diazo compound 20 and characterized by its IR and UVꢀvis spectra, and
the ESR spectra of the 2ꢀ, 3ꢀ, and 4ꢀquinolylcarbenes in propylenecarbonate, methylcyclohexane
12
or ethanol matrices at 6 K have been reported.
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The ESR spectrum of 2ꢀquinolylcarbene 25 (Z and E conformers) in Ar matrix at ~12 K
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has been obtained photolysis of 24T, and this photolysis also affords a small amount of 1ꢀ
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naphthylnitrene 35 (see Figure S2, Supporting Information). A strong ESR spectrum of 35 is
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obtained following FVP of 2ꢀ(5ꢀtetrazolyl)quinoline 22 at 500ꢀ600 C with deposition of the
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product in Ar matrix (Figure S3, Supporting Information). The same ESR spectrum of 35 is
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obtained by FVP of 24T or of 1ꢀnaphthyl azide at 500 C (Figure S4, Supporting Information). A
correlation between observed D values and calculated nitrene spin densities for several nitrenes,
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including 1ꢀnaphthylnitrene 35, is reported in the accompanying publication.
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2
ꢀQuinolylcarbene 25 was generated previously by conventional FVP of either the 2ꢀ(5ꢀ
tetrazolyl)quinoline 22 or 1,2,3ꢀtriazolo[1,5ꢀa]quinoline 24T and yielded virtually the same
results as described for 14 and 18, viz. a ca. 3:1 mixture of 3ꢀ and 2ꢀcyanoindenes 12 and 13
(
Schemes 3 and 4).
Reaction Mechanism
The formation of the cyanoindenes 12 and 13 in all cases as well as the direct observation of 1ꢀ
1
3
naphthylnitrene 35 in the FVP of 22 indicate the occurrence of a deepꢀseated rearrangement,
whereby 4ꢀquinolylcarbene 17 and 3ꢀquinolylcarbene 21 enter the energy surface already known
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4
to connect 2ꢀquinolylcarbene 25 and 1ꢀnaphthylnitrene 35 (Scheme 4).
Scheme 4. Rearrangements of 4ꢀ, 3ꢀ, and 2ꢀQuinolylcarbenes to 1ꢀNaphthylnitrene and
Cyanoindenes. Calculated Energies in kcal/mol at the B3LYP/6ꢀ31G* Level Relative to Openꢀ
Shell Singlet Nitrene 35 S = 0.
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Figure 1. The singlet energy surface for the 4ꢀ, 3ꢀ, and 2ꢀquinolylcarbenes 17, 21, and 25 and 1ꢀ
naphthylnitrene 35 (relative energies in kcal/mol at the B3LYP/6ꢀ31G* level (see continuation of
the energy surface in Figure 2).
The energies shown in Scheme 4 are translated into the energy profiles shown in Figures
1
and 2, where it is seen that the activation energies for these rearrangements are all very modest,
i.e. no more than ~20 kcal/mol with respect to the quinolylcarbenes and ~40 kcal/mol with
respect to the 1ꢀazaꢀbenzo[f]cycloheptatetraenes 27 and 33. Such barriers are very easily
accessed under FVP conditions. The openꢀshell singlet 1ꢀnaphthylnitrene 35 formed in this way
can now undergo ring contraction to 1ꢀcyanoindene 36 in a highly exothermic reaction with a
calculated barrier of 38 kcal/mol, and 36 interconverts with 3ꢀcyanoindene 12 and 2ꢀcyanoindene
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3 in a series of 1,5ꢀshifts of H and CN as described previously (Scheme 4 and Figure 2).
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Figure 2. Ring contraction of 1ꢀnaphthylnitrene to cyanoindenes (relative energies in
kcal/mol at the B3LYP/6ꢀ31G* level). For the interconversion of the cyanoindenes see refs. 7
and 9.
Although the triplet nitrene 35 T is the lowest energy minimum prior to formation of the
0
cyanoindenes, the 1ꢀazaꢀbenzo[f]cycloheptatetraene 27 and 33 are very close in energy to the
singlet nitrene 35 S (Figure 1). Compound 33 has been observed by IR spectroscopy under
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matrix photochemistry conditions from both the carbene side (23) and the nitrene side (27),
but it is very difficult to observe intermediates of this type under FVP conditions because of the
availability of favorable, exothermic reaction paths to the cyanoindenes. Furthermore, the FSꢀ
FVP method used here is not suitable for matrixꢀisolation of reactive intermediates.
Figures 1 and 2 present coherent and energetically feasible mechanism for the
rearrangement of the quinolylcarbenes to cyanoindenes. Nevertheless, several other potential
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reactions will now be considered. They are numbered (1)ꢀ(6) below.
(
1) Instead of cyclizing to the ring junction position, forming the transition state 26TS,
ꢀquinolycarbene 17 could also cyclize onto the 3ꢀposition, forming the cyclopropene 39
Scheme 5). Compound 39 has a relatively low energy virtually identical to that of 29, 15
kcal/mol. Ringꢀopening of 39 would lead to the orthoꢀquinonoid azaꢀbenzocycloheptatetraene
0, which lies 21 kcal/mol above 35 S . The corresponding singlet azacycloheptatrienylidene 41
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lies ca. 5 kcal/mol higher. Therefore, compounds 40 and 41 may well be formed in a reversible
manner, but it is not obvious how this could lead to the observed products, the cyanoindenes.
Scheme 5. Alternative Ring Expansion of 4-Quinolylcarbene 17 (Energies in kcal/mol at the
B3LYP/6-31G* Level Relative to 1-Naphthylnitrene 35 S1)
(2) 1,2ꢀHydrogen shifts of the type 40(41) → 27 (Scheme 6) would lead into the
mechanism described in Scheme 4 and Figure 1, but there is no firm evidence for the occurrence
of hydrogen shifts in cycloheptatetraenes/cycloheptatrienylidenes; if they were occurring, the
several carbon and deuterium labeling experiments that have been conducted would have
revealed them. Xie, Schreiner and coꢀworkers reported a very high, calculated, activation barrier,
of the order of 80 kcal/mol, for a 1,2ꢀH shift in a benzocycloheptatetraene (the allꢀcarbon
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analogue of 30 → 33), which is too high to make such shifts important. We have located two
transition states for the reaction 40(41) → 27 (Scheme 6) lying at 68.3 and at 83.5 kcal/mol
relative to 35 S at the B3LYP/6ꢀ31G* level. These two transition states are interesting in their
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own right. In 40TS1 an intact benzene ring is preserved, whereas 40TS2 is ortho-quiononoid
(Figure 3). Thus, these two transition states can be said to be bondꢀshift isomers. 40TS1 actually
connects the cycloheptatrienylidene 41 and the allene 27, whereas 40TS2 connects the two
allenes 40 and 27, whereby an inflexion point on the IRC curve suggests the reaction passes
through the carbene 27’ (see IRC curves in Figure S5, Supporting Information). Further
theoretical work on these hypothetical Hꢀshifts and transition states is planned, but the important
outcome as regards Scheme 6 is that the Hꢀshift 40 → 27 has a barrier of 50ꢀ65 kcal/mol (68ꢀ83
kcal/mol above 35 S ), which is drastically higher than any of the barriers in Figures 1 and 2.
1
This is illustrated energetically in Figure 4.
Scheme 6. Hypothetical, Non-Observed 1,2-H Shifts Connecting 40 and 27 (Energies in
kcal/mol at the B3LYP/6-31G* Level Relative to 1-Naphthylnitrene 35 S1)
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4
0TS1
40TS2
Figure 3. Calculated transition states for the hypothetical reactions 40(41)ꢀ27 (B3LYP/6ꢀ
31G*). Left: transition structure 40TS1 is benzeneꢀlike; the internal reaction coordinate (IRC)
graph connects carbene 41 with allene 27. Right: transition structure 40TS2 is oꢀquinonoid; the
IRC graph connects allene 40 with allene 27. See Figure S5 (Supporting Information).
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41
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48
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53
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55
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Figure 4. The carbene ring expansion 17 → 40 and the nonꢀobserved 1,2ꢀH shift 40 → 27 via
40TS1/40TS2 (energies in kcal/mol at the B3LYP/6ꢀ31G* level relative to 1ꢀnaphthylnitrene 35
S1).
(3) 3ꢀPyridylcarbene, 3ꢀpyridylnitrene and 3ꢀquinolylnitrene have all been shown to
4
,11
undergo ring opening to nitrile ylides. It was therefore necessary to enquire whether 3ꢀ
11
quinolylcarbene 21 could undergo analogous ring opening to the ylide 42 (Scheme 7). While
the reaction is computationally feasible, it would involve overall energies more than 10 kcal/mol
higher than those in Figure 1, and we have no experimental evidence for its occurrence.
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6
Scheme 7. Potential but Unobserved Ring Opening of 3-Quinolylcarbene 21 and 1-Aza-
benzocycloheptatetraene 27 (Energies in kcal/mol at the B3LYP/6-31G* Level Relative to
1-Naphthylnitrene 35 S1)
0
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(4) Cycloheptatetraenes are known to undergo transannular cyclization en route to ring
5
contraction to fulvenallene and benzofulvenallene, and analogous mechanisms have been put
forward for the rearrangements of 2ꢀpyridylcarbene and 1ꢀisoquinolylcarbene to
5,7
cyanocyclopentadienes and cyanoindenes, respectively. The azaꢀbenzocycloheptatetraene 30
could undergo a similar rearrangement to tricyclic compound 43 and then to the spiroazirine 44,
the biradical 45 and 1ꢀcyanoindene 36 as a mechanism for forming the cyanoindenes 12 and 13.
7
The energies of the intermediates 44, 45, and 36 have been calculated previously and are
repeated in Scheme 8.
Scheme 8. A potential route from 1-Aza-benzocycloheptatetraene 30 to Cyanoindenes
(Energies in kcal/mol at the B3LYP/6-31G* Level Relative to 1-Naphthylnitrene 35 S1)
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However, the first step in Scheme 8 requires a high activation energy of 54 kcal/mol relative to
nitrene 35 S (or 32 kcal/mol relative to 30), which puts it considerably above all the barriers in
1
Figures 1 and 2. It is in principle possible that this reaction could take place under highꢀ
temperature FVP conditions, but it is not energetically competitive, and we have no evidence for
its occurrence.
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50
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54
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56
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58
59
60
(
5) There exists a second energy surface for 1ꢀnaphthylnitrene 35 S , which can be
1
accessed photochemically and leads to the spectroscopically characterized zwitterionic cumulene
1
5
48 (a cyclic nitrile ylide) (Scheme 9 and Figure 5). This rearrangement may well take place in a
reversible manner under FVP conditions, since the required energies are quite low, and lower
than the maximum energies in Figure 1, but this path has not been established in the present
study – again because the exothermic rearrangement to the cyanoindenes drives the thermal
reaction. An analogous situation pertains to 9ꢀphenanthrylnitrene, which undergoes “normal”
ring expansion to a dibenzoazacycloheptatetraene (analogous to 33) on FVP but to a cyclic nitrile
1
7
ylide (analogous to 48) on photolysis.
1
5
Scheme 9. Alternative Ring Expansion of 1-Naphthylnitrene 35 S (Relative Energies in
1
kcal/mol at the B3LYP/6-31G* Level)
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0
Figure 5. Singlet energy surface for the ring expansion of 1ꢀnaphthylnitrene 35 S to the cyclic
1
1
5
nitrile ylide 48 (relative energies in kcal/mol at the B3LYP/6ꢀ31G* level).
(6) The rearrangement of 1ꢀisoquinolylcarbene 9 to 2ꢀnaphthylnitrene and to 3ꢀ and 2ꢀ
7
cyanoindenes (Scheme 2) is analogous to that of 2ꢀquinolylcarbene to 1ꢀnaphthylnitrene and the
cyanoindenes. The two energy surfaces are formally linked through 1ꢀcyanoindene 36, but
otherwise there is no known connection between them. Whereas 1ꢀ and 2ꢀnaphthylcarbenes
1
6
interconvert via ring expansion to benzocycloheptatetraene, 1ꢀ and 2ꢀnaphthylnitrenes do not
5
interconvert, just as phenylnitrene does not undergo a “ringꢀwalk” process.
Conclusion
The cyanoindenes 12 and 13 are the end products of the thermolysis reactions designed to
generate the 4ꢀ, 3ꢀ, and 2ꢀquinolylcarbenes. Calculations of the structures and energies of
intermediates and transition states at the B3LYP/6ꢀ31G* level support the postulated
rearrangement of 4ꢀquinolylcarbene 17 to 3ꢀquinolylcarbene 21 to 2ꢀquinolylcarbene 25 to 1ꢀ
naphthylnitrene 35 and then to 3ꢀ and 2ꢀcyanoindenes 12 and 13. The calculated activation
barriers (Figures 1 and 2) are readily accessible under the flash vacuum pyrolysis conditions
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employed. In contrast, the potential 1,2ꢀH shifts in azaꢀbenzocycloheptatetraenes or azaꢀ
benzocycloheptatrienylidenes 40, 41, and 27 have very high calculated activation energies
(Figures 3 and 4) and are not observed.
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Computational Method
All calculations were performed using the Gaussian 03 suite of programs. Reported energies
298.15 K) include zeroꢀpoint vibrational energy corrections. Transition states were verified by
1
8
(
intrinsic reaction coordinate calculations. Imaginary frequencies are reported in the Supporting
Information. The energies of the openꢀshell singlet nitrene 35 S and carbenes 41 and 27’ were
1
computed at the UB3LYP/6ꢀ31G* level and corrected using the sum method of Cramer and
Ziegler as E(S ) = 2 E(50:50) − E(T ), where E(50:50) is the energy of the brokenꢀsymmetry
1
0
2
unrestricted wave function with an expectation value <S > = 1, and E(T ) is the energy of the
0
1
9
triplet state.
Experimental Section
The apparatus used for conventional, preparative flash vacuum pyrolysis (FVP), falling solid
2
0
1
0,21
FVP (FSꢀFVP),
and FVP coupled to a liquid nitrogen cryostat for IR or ESR spectroscopic
21
observation at 77 K have been described and correspond to Figures 3b, 11 and 5, respectively,
1
13
in ref. 20. H NMR spectra were recorded at 400 MHz, and C NMR spectra at 25 MHz. Mass
spectra were obtained using electron ionization at 70 eV and recorded on a conventional sector
instrument.
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5
-(3-Quinolyl)tetrazole 18
A mixture of 3ꢀcyanoquinoline (4.5 g; 29.25 mmol), 1.9 g (29.25 mmol) NaN , and 1.35 g (29.25
3
o
mmol) NH Cl in 150 mL dry DMF was stirred under dry N for 10 days at 120 C, after which
4
2
0
1
2
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0
time the solvent was removed in vacuo, and the oily residue was treated with 100 mL 15% HCl
ꢀ2
with stirring. The tetrazole which precipitated was filtered and dried at 10 hPa at RT to yield
o
1
5.3 g (92%) of white crystals, mp 252 C (decomposition). H NMR (DMSOꢀd ) 9.67 (d, J = 2
6
Hz, 1H), 9.39 (d, J = 2 Hz, 1H), 8.28 (d, J = 8 Hz, 1H), 8.23 (d, J = 8 Hz, 1H), 8.01 (dt, J = 2
1
3
and 8 Hz, 1H), 7.83, t, J = 8 Hz, 1H), 5.7 (very broad, ca. 1H). C NMR (DMSOꢀd ) 153.9,
6
+
146.1, 143.8, 138.2, 133.0, 129.3, 128.9, 127.4, 125.7, 118.8. MS m/z (%) 198 (2), 197 (M ⋅,
1
7), 170 (4), 169 (35), 154 (7), 142 (8), 115 (9), 38 (99), 37 (11), 36 (100), 35 (39). IR (KBr)
3100ꢀ2100 (very broad), 1630 s, 1580 s, 1530 s, 1385 s, 1365 s, 1305 s, 1225 s, 1210 s, 1090 s,
ꢀ1
1
060 s, 1025 s, 940 s, 865 vs, 650 s, 765 s cm . Anal. Calcd for C H N : C, 60.91; H, 3.58; N,
1
0
7
5
35.51. Found: C, 60.84; H, 3.44; N, 35.36.
Pyrolysis of 5-(3-Quinolyl)tetrazole 18
A sample of 1 g of the solid, powdered tetrazole was subjected to FSꢀFVP at 600 C at a pressure
o
ꢀ3
ꢀ1
varying between 10 and 10 hPa in the course of 60 min. The resulting products were separated
o
1
by preparative GC (SE52, 160 C isothermally) and identified by direct comparison of the H
9
,21
NMR, IR and mass spectra with those of the compounds isolated previously.
products were obtained (relative yields by GC): 3ꢀcyanoquinoline 19 (57%), 2ꢀcyanoindene 13
12%), 3ꢀcyanoindene 12 (28%). A trace of an additional compound (0.8%), possibly 1ꢀ
cyanoindene, was also present.
The following
(
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ꢀCyanoindene 13: H NMR (CDCl ) 3.68 (d, J = 1.9 Hz, 2H), 7.60 (t, J = 1.9 Hz, 1H), 7.51ꢀ
3
ꢀ1
+
7
.37 (m, 4H). IR (film on KBr) 2215 cm . MS m/z (%) 142 (10), 141 (M ⋅, 100), 140, (54), 114
(22), 113 (10).
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35
36
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44
45
46
47
48
49
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60
1
3
ꢀCyanoindene 12: H NMR (CDCl ) 3.62 (d, J = 2.0 Hz, 2H), 7.59 (t, J = 1.7 Hz, 1H), 7.51 (d, J
3
= 7.5 Hz, 1H), 7.40 (t, J = 7.5 Hz, 1H), 7.34 (t, J = 7.5 Hz, 1H), 7.30 t, J = 2.0 Hz, 1H). IR (film
ꢀ1
+
on KBr) 2230 cm . MS m/z (%) 142 (43), 141 (M ⋅, 100), 140 (100), 114 (72), 113 (34).
5-(4-Quinolyl)tetrazole 14
This compound was prepared from 4ꢀcyanoquinoline (1.0 g; 6.5 mmol) in the same manner as
described for 18 above and obtained as white crystals (1.0 g; 78%) after recrystallization from
o
1
waterꢀethanol (1:1), mp 235 C (decomposition). H NMR (DMSOꢀd ) 9.29 (d, J = 5.0 Hz, 1H),
6
9
.03 (d, J = 8.7 Hz, 1H), 8.37 (d, J = 5.0 Hz, 1H), 8.35 (d, J = 8.7 Hz, 1H), 8.06 (dt, J = 8.7 Hz,
1
3
1
H), 7.93, t, J = 8 Hz, 1H), 5.7 (very broad, ca. 1H). C NMR (DMSOꢀd ) 156.2, 146.4, 141.6,
6
+
1
36.4, 133.2, 130.0, 126.7, 124.3, 124.0, 121.2. MS m/z (%) 198 (10), 197 (M ⋅, 99), 170 (13),
1
69 (100), 168 (7), 154 (15), 143 (7), 142 (54), 141 (4), 140 (6), 129 (7), 128 (19), 127 (16), 115
(16), 101 (26), 84 (15), 75 (16), 63 (23), 38 (26), 36 (93). IR (KBr) 2900ꢀ2100 (very broad),
1
625 m, 1595 s, 1540 m, 1380 s, 1320 m, 1270 m, 1225 s, 1210 s, 1020 s, 1005 s, 920 m, 830 s,
ꢀ1
8
10 s, 755 s, 695 m cm . Anal. Calcd for C H N : C, 60.91; H, 3.58; N, 35.51. Found: C, 61.07;
10 7 5
H, 3.69; N, 35.41.
Pyrolysis of 5-(4-Quinolyl)tetrazole 14
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o
A sample of 0.5 g of the solid, powdered tetrazole was subjected to FSꢀFVP at 600 C at a
ꢀ3
ꢀ1
pressure varying between 10 and 10 hPa in the course of 60 min. The resulting products were
1
identified by direct comparison of the GC, H NMR, IR and mass spectral data with those
0
1
2
3
4
5
6
7
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9
0
1
2
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0
9,22
obtained for the pyrolysis of 18.
The product composition was nearly identical with that
obtained in the FVP of 18: 4ꢀcyanoquinoline 19 (61%), 2ꢀcyanoindene 13 (10%), 3ꢀcyanoindene
2 (26%). A trace of an additional compound, possibly 1ꢀcyanoindene, was also present.
1
Pyrolysis of 5-(2-Quinolyl)tetrazole 22 and 1,2,3-Triazolo[1,5-a]quinoline 24T
9
The preparation and conventional FVP of 22 and 24T were described previously. Pyrolysis of
2
1
2
2 and 24T in the apparatus for low temperature (77 K) IR spectroscopy allowed the detection
ꢀ1
of an absorption ascribed to 2ꢀdiazomethylquinoline 24D (2070 cm ; Figure S1aꢀb, Supporting
ꢀ1
Information), as well as 3ꢀ and 2ꢀcyanoindenes 12 and 13 (2230 and 2215 cm , respectively;
Figure S1bꢀc). When 22 was the starting material, partial cycloreversion to HN and 2ꢀ
3
cyanoquinoline was also observed (Figure S1b).
ASSOCIATED CONTENT
Supporting Information Available. Figures showing IR absorption assigned to 2ꢀ
diazomethylquinoline 24D, ESR spectra of 2ꢀquinolylcarbene 25 and 1ꢀnaphthylnitrene 35, IRC
graphs for 40→27 and 41→27, Computational method, Cartesian coordinates, energies, and
imaginary frequencies, where relevant, of calculated structures. This material is available free of
charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Curt Wentrup. Eꢀmail: wentrup@uq.edu.au
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Notes
The authors declare no competing financial interest.
Acknowledgment. This research was supported by the Deutsche Forschungsgemeinschaft
(We774/4A), the Australian Research Council (DP0770863), the National Computing
Infrastructure facility financed by the Australian Government (MAS g01) and the Queensland
Cyber Infrastructure Foundation at The University of Queensland (QCIFg01).
References
1
(a) Wentrup, C. Acc. Chem. Res. 2011, 44, 393ꢀ404. (b) Wentrup, C. Matrix Studies on
Aromatic and Heteroaromatic Nitrenes and their Rearrangements. In Nitrenes and Nitrenium
Ions (Falvey, D. E.; Gudmundsdottir, A. D., Eds.), John Wiley & Sons: Hoboken, NJ 2013,
Chapter 8, pp 273ꢀ315. (c) Sheridan, R. S. Chem. Rev. 2013, 113, 7179ꢀ7208.
2
(a) Wentrup, C. Top. Curr. Chem. 1976, 62, 173ꢀ251. (b) Kemnitz, C. R.; Karney, W. L.;
Borden, W. T. J. Am. Chem. Soc. 1998, 120, 3499.
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(a) Chapman, O. L.; Sheridan, R. S.; LeRoux, J. P. J. Am. Chem. Soc. 1979, 101, 3690. (b)
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Kvaskoff, D.; Lüerssen, H.; Bednarek, P.; Wentrup, C. J. Am. Chem. Soc. 2014, 136, 15203.
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Crow, W. D.; Khan, A. N.; PaddonꢀRow, M. N.; Sutherland, D. S. Aust. J. Chem. 1975, 28,
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Wentrup, C.; Thétaz, C.; Lüerssen. H.; Aylward, N.; Kvaskoff, D. J. Org. Chem. 2016, 81,
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Bégué, D.; Qiao, G. G.; Wentrup, C. J. Am. Chem. Soc. 2012, 134, 5339.
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Wentrup, C.; Becker, J.; Winter, H.ꢀW. Angew. Chem. Int. Ed. 2015, 54, 5702.
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Kvaskoff, D.; Mitschke, U.; Addicott, C.; Bednarek, P.; Finnerty, J.; Wentrup, C. Aust. J.
Chem. 2009, 62, 275.
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(a) Hutton, R. S.; Roth, H. D.; Schilling, M. L. M.; Suggs, J. W. J. Am. Chem. Soc. 1981, 103,
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Maltsev, A.; Bally, T.; Tsao, M.ꢀL.; Platz, M. S.; Kuhn, A.; Vosswinkel, M.; Wentrup, C.
J. Am. Chem. Soc. 2004, 126, 237.
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6
Xie, Y.; Schreiner, P. R.; Schleyer, P. von R.; Schaefer, H. F., J. Am. Chem. Soc. 1997, 119,
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