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Synthesis 2007(15): 2351-2359  
DOI: 10.1055/s-2007-983793
PAPER
© Georg Thieme Verlag Stuttgart · New York

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

Peiling Chena, Patrick J. Carrollb, 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
Further Information

Publication History

Received 8 March 2007
Publication Date:
12 July 2007 (online)

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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

10

See ref. 6

11

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).

13

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.