Singlet and triplet photocycloaddition reactions of 2‐pyridones with propenoate and 2,4‐pentadienotes, and the frontier molecular orbital analysis

Abstract

Regioselective photocycloadditions of 2‐pyridones (1) with 2,4‐pentadienoates (3) were analysed and compared with the reactions with propenoate (2), and origins of the different regioselectivities were inferred from frontier molecular orbital properties by the use of PM3‐CI method. Direct photoreactions of 1 with 3 being α,β,γ,δ‐unsaturated carboxylates gave four types of regio‐selective [2+2]cycloadducts, 3‐β:4‐α‐4, 5, 3‐δ:4‐γ‐6,7,5‐δ: 6‐γ‐8, 9 and 5‐δ:6‐γ‐[2+2]cycloadducts 10,11. Sensitized photoreactions of 1 with 3 did not occur, and fluorescence of 1 was weakly quenched by 3. Otherwise, main cycloadducts in the sensitized reactions of 1 with 2 have been obtained as 5‐α:6‐β‐[2+2]cycloadducts, which were different from main 3‐β:4‐α‐[2+2]cycloadducts of the direct reactions, and these site‐and regio‐selectivities were inferred from the different frontier molecular orbital coefficients at the. 3‐and 6‐positions of 1 for the triplet and singlet states. Formations of 4–7 were also interpreted by both effects of frontier orbital HSOMO‐LUMO interactions and of the electrostatic interaction between 1 and 3. The other site‐and regioselective adducts 8–11 were inferred to be formed by the electrostatic interactions similar to 2‐pyridone photodimerization.

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

“…Somekawa and co-workers studied the [2 + 2] photocycloaddition of 2-pyridones both in its intermolecular 705 and its intramolecular 706 version. The regioselectivity of the intermolecular [2 + 2] photocycloaddition is variable and, like for the related 2-pyrones, it is complicated by [4π] photocyclization, [4 + 4] photodimerization, and formal [4 + 2] cycloaddition reactions.…”

Photochemical Cleavage Reactions of 8-Quinolinyl Sulfonates in Aqueous Solution

“…BZ is a well-known sensitizer that has a tripletstate energy (E T ) value of 69 kcal mol Ϫ1 and brings about the triplet-state (T 1 ) of the substrates by energy transfer from the triplet state of BZ (BZ*(T 1 )). [44][45][46][47][48][49] The E T value of 5a was estimated to be 61 kcal mol Ϫ1 from its phosphorescence spectra in a frozen MeCN/H 2 O. Upon photoirradiation of a mixture of 1 mM of 5a and 10 mM of BZ in CD 3 CN/D 2 O (10 mM HEPES at pD 7.4) (90/10) for 15 min at 355 nm, which is absorbed only by BZ, photolysis of 5a proceeded in ca.…”