Photoinduced H‐Abstraction in Homo‐ and Protoadamantylphthalimide Derivatives in Solution and in Organized and Constrained Media

Abstract

The photochemical reactivity of homoadamantylphthalimide 5 and protoadamantylphthalimides 9 and 10 was investigated in solution, in the β‐cyclodextrin (CD) complex, and in the solid state. The triplet excited states of 5, 9 and 10 were characterized by laser flash photolysis. Sensitized irradiation in solution was found to give rise to polycyclic products through a transiently generated higher excited triplet state, not detectable by LFP. Direct excitation of 5, 9 and 10 gives, in addition to the products arising from the triplet state, cleavage products probably generated through a singlet state. Complexation with β‐cyclodextrin changes the regiochemistry of H‐abstraction. In the solid state, 5 and 9 are both photoreactive though state‐dependent product mixtures are noted. Irradiation of 5 affords only one product whereas irradiation of 9 affords the same product mixture regardless of whether irradiation is performed in the solid state or in CH3CN solution.

[3 + 2] Cycloaddition with photogenerated azomethine ylides in β-cyclodextrin

“…However, for the adamantane derivative in the presence of β-CD, the secondary photochemical H-abstraction became more efficient, resulting in a different product distribution. More efficient H-abstraction reaction in the presence of β-CD have been reported [16].…”

“…We became interested in the application of photochemical H-abstraction reactions initiated by phthalimides in organic synthesis [14,15]. Furthermore, H-abstractions were investigated in inclusion complexes, in the cavity of β-cyclodextrins (β-CD) [16]. We found out that H-abstraction reactions were about ten times more efficient in the β-CD complexes than in the isotropic solution, and the macrocyclic host affected the stereochemistry of the reaction.…”

Mechanistic Studies of Adamantylacetophenones with Competing Reaction Pathways in Solution and in the Crystalline Solid State

“…The reaction mixture was poured into a solution of 50 mL of H 2 O and 2 mL of 2 M HCl, extracted with DCM, dried over MgSO 4 , and evaporated to give the crude product as a white solid, which was purified by flash chromatography (SiO 2 , 4:1 hexanes/ethyl acetate) to give 10 as a white powder (871 mg, 97% yield): R f = 0.0.35 (4:1 hexanes/ethyl acetate); mp 292−294 °C (lit. 4 (6). A 35 mL roundbottom flask was charged with 10 (200 mg, 0.69 mmol), DCM (10 mL), and DMF (1 drop).…”

“…Dry CO 2 was then bubbled through the solution for 10 min, with the cold bath being removed after the first 5 min. The reaction mixture was poured into a solution of 50 mL of H 2 O and 2 mL of 2 M HCl, extracted with DCM, dried over MgSO 4 , and evaporated to give the crude product as a white solid, which was purified by flash chromatography (SiO 2 , 4:1 hexanes/ethyl acetate) to give 10 as a white powder (871 mg, 97% yield): R f = 0.0.35 (4:1 hexanes/ethyl acetate); mp 292–294 °C (lit . 291–293 °C); IR (film) 2959, 1694, 1603, 1459, 1390, 1363, 1287, 1218, 1165, 1083, 909, 878, 745 cm –1 ; 1 H NMR (500 MHz, CDCl 3 ) δ 7.45 (s, 2H), 1.49 (s, 18H), 1.33 (s, 9H); 13 C­{ 1 H} NMR (126 MHz, CDCl 3 ) δ 180.3, 150.9, 146.5, 127.7, 122.3, 37.2, 35.2, 32.4, 31.4; HRMS (APCI, quadrupole-orbitrap) m / z [M + H] + calcd for C 19 H 31 O 2 291.2319, found 291.2308.…”

“…The Norrish type II reaction is one of the most widely studied photochemical processes, and many mechanistic studies of a broad range of compounds both in solution and in the solid state have been reported. − In a recent study, crystals of adamantyl- p -methoxy-acetophenone [ 1 (Figure )] were utilized for one of the first mechanistic investigations of the Norrish type II reaction based on absolute photochemical kinetics in the solid state using laser flash photolysis (LFP) of aqueous nanocrystalline suspensions . Along with the identification of transient intermediates and their lifetimes, it was shown that the photoproduct diastereoselectivity for 1 is affected by the rotation of the globular adamantane group, which occurs both in solution and in the solid state.…”