Intramolecular Reactivity of trans [4+4] Photodimers of 2-Pyridones

Peiling Chen; Patrick J. Carroll; Scott Mc N. Sieburth

doi:10.1055/s-2007-983793

PAPER

Intramolecular Reactivity of trans [4+4] Photodimers of 2-Pyridones

Peiling Chen^a, Patrick J. Carroll^b, Scott McN. Sieburth*^a
^a Department of Chemistry, Temple University, 1901 N. 13th St., Philadelphia, PA 19122, USA
e-Mail: scott.sieburth@temple.edu;
^b Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA

Abstract

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Abstract

Photodimers of 2-pyridones are cycloocta-1,5-dienes with two lactam bridges. These, and related structures, undergo halogenation to give rearranged products in which an amide nitrogen has intercepted an initial halonium ion. For the trans isomer, a transient four-membered azetidinium ion reacts via dealkylation, giving a dihalide-diamide product in high yield. This readily available intermediate reacts with nucleophiles in a process that begins with intramolecular amide N-alkylation, reforming the azetidinium intermediate. Reaction of this intermediate with the nucleophile can take two different paths, depending on the reversibility of the nucleophilic attack, with reversible nucleophiles giving N-dealkylation and irreversible nucleophiles reacting with the carbonyl group.

Key words

cycloadditions - dimerizations - ketones - photochemistry - pyridines

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References

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Compound 10a crystallized in the rhombohedral space group R-3, with a = 25.354 (2) Å, b = 25.354 (2) Å, c = 18.437 (2) Å, and Z = 18. Direct solution using 4159 unique reflections with SHELXL-97 gave a final R ₁ = 0.0707 and R ₂ = 0.1980.

12

This structure was calculated by initially building a structure with a carbon atom in place of the positively charged nitrogen, and minimizing the structure using molecular mechanics. The resulting structure was then modified by replacing the carbon with a positively charged nitrogen and minimizing the structure using PM3 (MOPAC). The calculation was performed using WebMO (www.webmo.net). Images were generated with PyMOL (pymol.sourceforge.net).

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Compound 18a crystallized in the monoclinic space group P2₁/n, with a = 8.8752 (11) Å, b = 16.318 (2) Å, c = 13.575 (2) Å, β = 90.9270 (10)°, V = 1965.7 (5) Å³, and Z = 4. Direct solution using 3180 unique reflections with SHELXL-97 gave a final R ₁ = 0.0372 and R ₂ = 0.0816. Compound 19a crystallized in the orthorhombic space group Pca2₁, with a = 20.5701 (10) Å, b = 9.1456 (4) Å, c = 16.8463 (8) Å, V = 3169.2 (3) Å³, and Z = 8. Direct solution using 6546 unique reflections with SHELXL-97 gave a final R ₁ = 0. 0316 and R ₂ = 0. 0794.

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