by 13C NMR shift correlation and 1J(C,H) measurements.12 No
insertion product 4 is found.
Scheme 1
Compounds 5 and 7 are formed by addition of phenylni-
trene to the benzene ring of one of the four quinoxalines.
Alternative reaction pathways of the nitrene obviously are
blocked due to the lack of diffusion inherent to the solid
state. The observed addition is unique, as phenylnitrene
generated photolytically from phenyl azide fails to add to
benzene, aside from intramolecular additions.13 We ascer-
tained that quinoxaline (10 equiv) is not attacked by
phenylnitrene during irradiation of phenyl azide (42 × 10-3
M, λ > 300 nm, 18 h, 283 K) in benzene. Instead aniline
and azobenzene are formed in 17 and 9% yield, respectively.
Upon heating, the two “azanorcaradiene” subunits in 5 and
7 undergo a rearrangement to 1H-azepine 8 in the solid state,
probably via 1,5-sigmatropic nitrogen migration to 9 and
subsequent valence isomerization (Scheme 3).14 Solid phase
Compound 4 derives from a highly regioselective C-H
insertion of phenylnitrene into one of the C-H bonds of the
alkyl chains of the cavitand. Most probably, it is formed by
azide 1 embedded either in the interstitial volume of the
lattice or within the alkyl chains of 2 with the N3 moiety
pointing toward the resorcinarene skeleton.5b The remarkable
yield of 4 demonstrates the higher regioselectivity of solid-
state photoreactions compared to their solution counterparts.
Thermal treatment (112 °C for 35 min at 1 atm) of the
1.5:1 complex gives the 1:1 complex.10
Scheme 3
photolysis of 8 (λ > 300 nm, 5 h) affords back the two
aziridines 5 and 7 in quantitative yield in a ratio of 1:5,
presumably following a nonconcerted mechanism.
Photolysis of the 1:1 complex 1@2 under the same conditions
as above affords the diastereomeric aziridines 5 and 7 in a
combined yield of 38% as well as azobenzene (3) (Scheme 2).
In summary, utilizing the improved reaction behavior of
phenylnitrene in the solid state, we are able to offer an alter-
native to the multistep building of functionalized resorcin[4]arene
cavitands.15 The regioselective modification of cavitand 2 is
controlled via thermal treatment before UV irradiation of the
solid-state complex 1@2. N-Alkylaniline 4 and aziridines 5 and
7, respectively, are accessible in good yield, in contrast to the
generally low yield reactions of phenylnitrene in solution. The
ratio of 5 to 7 can be reversed by valence isomerization to 1H-
azepine 8 and subsequent UV irradiation.
Scheme 2
Acknowledgment. We are indebted to the FWF in
Osterreich (Project No. P12533-CHE) for financial support.
¨
Supporting Information Available: Experimental pro-
cedures and details of NMR and X-ray diffraction (CIF)
studies. This material is available free of charge via the
The structures 5 and 7 were assigned based on 2D NMR studies.
The fact that one of the aziridine protons (H-17) of 5 shows a
NOE signal to H-20 (see the Supporting Information, Table
S2, column D) suggests that the three-membered ring protons
H-17 and H-18 are pointing inward the cavity. This signal is
absent for 7 implying that the aziridine protons are pointing
outward the cavity. We excluded the isomeric 1-phenyl-3a,7b-
dihydropyrrolo[3′,2′:3,4]cyclobuta[1,2-b]pyrazine11 substructure
OL901122H
(11) (a) Yamada, S.; Sato, S.; Ohashi, M. J. Chem. Soc., Chem. Commun.
1984, 1643. (b) Ahmed, M.; Vernon, J. M. J. Chem. Soc., Chem. Commun.
1976, 462.
(12) 1J(C,H) ) 152, 163 and 155, 163 Hz for the aziridine rings in 5 and 7,
respectively. For further details, see the Supporting Information.
(13) (a) Doering, W. v. E.; Odum, R. A. Tetrahedron 1966, 22, 81. (b)
Sundberg, R. J.; Smith, R. H., Jr. Tetrahedron Lett. 1971, 3, 267. (c)
Sugawara, T.; Iwamura, H. J. Am. Chem. Soc. 1985, 107, 1329.
(14) (a) Lange, W.; Tu¨ckmantel, W. Chem. Ber. 1989, 122, 1765. (b)
Motyka, L. A. Tetrahedron Lett. 1985, 26, 2827. (c) Ikeda, M.; Ohno, K.;
Uno, T.; Tamura, Y. Tetrahedron Lett. 1980, 21, 3403.
(15) Roncucci, P.; Pirondini, L.; Paderni, G.; Massera, C.; Dalcanale,
E.; Azov, V. A.; Diederich, F. Chem. Eur. J. 2006, 12, 4775 and citations
therein.
(10) Again, the DSC analysis provides evidence for a two-step dis-
sociation process. Two-thirds of 1 are released at 145 °C with ∆H ) 16.6
kcal/mol. This process is significantly more endothermic than the dissocia-
tion of the 1:1 complex before heating the probe. Most probably, the thermal
treatment leads to a thermodynamically more favorable modification of the
crystal lattice. The remaining phenyl azide (1) is released at 169 °C (∆H )
2.2 kcal/mol).
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Org. Lett., Vol. 11, No. 14, 2009