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. 2011:7:1663-70.
doi: 10.3762/bjoc.7.196. Epub 2011 Dec 13.

Photochemical and thermal intramolecular 1,3-dipolar cycloaddition reactions of new o-stilbene-methylene-3-sydnones and their synthesis

Kristina Butković  1 , Zeljko Marinić, Krešimir Molčanov, Biserka Kojić-Prodić, Marija Sindler-Kulyk
Affiliations

Photochemical and thermal intramolecular 1,3-dipolar cycloaddition reactions of new o-stilbene-methylene-3-sydnones and their synthesis

Kristina Butković et al. Beilstein J Org Chem. 2011.

Abstract

New trans- and cis-o-stilbene-methylene-sydnones 3a,b were synthesized by transforming the trans- and cis-o-aminomethylstilbene derivative, obtained by reduction of corresponding o-cyano derivatives, into glycine ester derivatives (43 and 31% yield) followed by hydrolysis (90 and 96% yield), nitrosation and ring closure with acetic acid anhydride (30 and 40% yield). The products were submitted to photochemical and thermal intramolecular [3 + 2] cycloadditions to afford diverse heteropolycyclic compounds. Photochemical reactions afforded cis-3-(4-methylphenyl)-3a,8-dihydro-3H-pyrazolo[5,1-a]isoindole (11, 12.5% yield) and trans-3-(4-methylphenyl)-3a,8-dihydro-3H-pyrazolo[5,1-a]isoindole (12, 5% yield). Thermal reactions afforded 3-(4-methylphenyl)-3,3a,8,8a-tetrahydroindeno[2,1-c]pyrazole (14, 50% yield) and 11-(4-methylphenyl)-9,10-diazatricyclo[7.2.1.0(2,7)]dodeca-2,4,6,10-tetraene (15, 22% yield).

Keywords: [3 + 2] cycloaddition; isoindoles; nitrile imines; pyrazoles; sydnones.

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Figures

Figure 1
Figure 1
Resonance structures of the sydnone ring.
Scheme 1
Scheme 1
Thermal and photochemical intermolecular [3 + 2] cycloadditions.
Figure 2
Figure 2
Illustration of intramolecular [3 + 2] cycloadditions.
Figure 3
Figure 3
Styryl-sydnone 1 and stilbenyl sydnone 2 and their photoproducts F and G, respectively; target molecules 3 in this work.
Scheme 2
Scheme 2
Synthesis of the target molecules 3a and 3b.
Scheme 3
Scheme 3
Photolysis of cis- or trans-3.
Scheme 4
Scheme 4
Aromatization with DDQ.
Scheme 5
Scheme 5
Possible mechanism for the formation of the photoproducts.
Scheme 6
Scheme 6
Thermal reaction of trans-3.
Figure 4
Figure 4
ORTEP of compound 14.
Scheme 7
Scheme 7
Thermal reaction of cis-3.
Figure 5
Figure 5
Proposed stereochemical pathway of sydnone ring (CH–N) and trans- and cis-stilbene (α–β).
Figure 6
Figure 6
Proposed stereochemical pathway of sydnone ring (N–CH) and trans- and cis-stilbene (α–β).
Scheme 8
Scheme 8
Possible formation of thermal products 14 (from trans-3) and 15 (from cis-3).
See this image and copyright information in PMC

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