Photocleavage Reactions of Monothioimides

Fu, T. Y.; Scheffer, John R.; Trotter, James

doi:10.1107/s0108270197011645

Cited by 3 publications

(4 citation statements)

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“…Accordingly, ketones 1a − i (Scheme ) were prepared by standard procedures that are outlined in the Experimental Section. Of these, compounds, 1a and 1c were previously known; 12a,13a,b the remainder represent new compounds that are reported here for the first time. We also thought it worthwhile to extend the study to analogues of ketones 1a − i and chose as our target molecules the 2-methyl-2-adamantyl phenyl ketones 5a − g (Scheme ).…”

Section: Resultsmentioning

confidence: 89%

“…The synthesis of ketones 5a − g , all of which are new, is outlined in the Experimental Section. All 16 ketones prepared for the present study were crystalline, and of these, 10 had their crystal and molecular structures determined (ketones 1a , 1b , 1c , 1f , 1h , 1i , 5a , 5c , 5d , and 5g ); details of the crystal structure determination for ketone 1c have been published 13c. None of the ketones whose crystal structures were determined crystallized in chiral space groups, thus precluding absolute asymmetric synthesis studies.…”

Section: Resultsmentioning

confidence: 99%

“…Preparation of Starting Materials. Ketone 1a was prepared as described by Padwa and Eastman,13b and ketone 1c was prepared according to the procedure of Lewis et al12a As far as we are aware, the remainder of the starting materials described below are new.…”

Section: Methodsmentioning

confidence: 99%

“…cis -4- tert -Butylcyclohexyl p -fluorophenyl ketone (1b) was prepared as described for ketone 1a ,13b except that fluorobenzene was used instead of benzene in the Friedel−Crafts reaction. Recrystallization of the crude product from methanol afforded colorless plates: mp 82−84 °C, in a yield of ∼57%; 1 H NMR (CDCl 3 ) δ 7.99−7.82 (2H, m, ArH), 7.18−7.02 (3H, m, ArH), 3.52−3.41 (1H, m, α-CH) 2.22−2.09 (2H, m), 1.72−1.50 (4H, m), 1.36−1.11 (3H, m), 0.80 (9H, s, C(CH 3 ) 3 ); 13 C NMR (CDCl 3 ) δ 23.34 (+), 27.46 (−), 28.27 (+), 32.52 (+), 40.32 (−), 48.06 (−), 115.28 and 115.70 ( 2 J C - F = 21 Hz, −ve), 130.66 and 130.84 ( 3 J C - F = 9 Hz, −ve), 133.11 and 133.17 ( 4 J C - F = +ve), 162.71 and 167.74 ( 1 J C - F = 253 Hz, +ve), 202.60 (+); IR (KBr) 2923, 2856, 1675 (CO), 1599, 1508, 1467, 1453, 1407, 1393, 1365, 1345, 1302, 1217, 1171, 1158, 1142, 974, 908, 856, 828, 791, 661, 607, 559, 522, 484 cm -1 ; UV (hexane) 242 (15 500), 269 (3320), 325 (110) nm; MS (EI) m / z 263, 262 (M + ), 247, 205, 165, 151, 138, 124, 123 (100), 112, 109, 95, 83, 75, 69, 57, 55, 41, 32; HRMS (EI) m / z 262.1734 (calcd for C 17 H 23 OF, 262.1733).…”

Section: Methodsmentioning

confidence: 99%

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An Investigation of the Yang Photocyclization Reaction in the Solid State: Asymmetric Induction Studies and Crystal Structure−Reactivity Relationships

et al. 1998

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The Norrish/Yang type II photochemistry of 16 ketones having the basic cis-4-tert-butyl-1benzoylcyclohexane or 2-benzoyladamantane structure has been investigated in the solid state and solution. In both media, ketones bearing methyl substituents R to the benzoyl group undergo stereoselective Yang photocyclization to afford endo-arylcyclobutanols. Quantum yield and quenching studies in solution show that the reactions are efficient triplet-mediated processes. Asymmetric induction studies were carried out by providing the reactants with carboxylic acid substituents to which "ionic chiral auxiliaries" were attached through salt formation with optically active amines. Irradiation of the salts (17 in total) in solution gave racemic cyclobutanols, but in the crystalline state, moderate to near-quantitative enantiomeric excesses were obtained. Single crystal X-ray diffraction studies were successfully performed on 10 neutral ketones and four salts. This allowed the reactive γ-hydrogen atoms to be identified and the distance and angular parameters associated with their abstraction to be tabulated. For the 14 compounds whose crystal structures were determined, the average value of d, the CdO‚‚‚H abstraction distance, was 2.61 ( 0.07 Å, and the values of ω (the γ-hydrogen out-of-plane angle), ∆ (the CdO‚‚‚H γ angle) and θ (the C-H γ ‚‚‚O angle) were 53 ( 11, 84 ( 7, and 115 ( 2°, respectively. In a similar manner, the geometric parameters associated with the ring closure reactions of the intermediate 1,4-hydroxy biradicals were estimated from the crystallographic data. This indicates that the biradicals are 66.5 ( 9.8 and 32.7 ( 3.2°out of alignment for cleavage, but that they are well oriented for cyclization, with radical separations (D) of 3.08 ( 0.09 Å. For one of the salts in the adamantane series, the solid-state photoreaction was shown to be topotactic; that is, a single crystal of the reactant salt was transformed quantitatively into a single crystal of the corresponding cyclobutanol salt. Since the absolute configuration of the ionic chiral auxiliary in this case was known, this permitted the absolute steric course of the reaction to be mapped by X-ray crystallography and the abstracted γ-hydrogen to be identified unequivocally. In addition, the crystal structure of a partially reacted crystal containing 60% product and 40% reactant was successfully determined. This showed that the two compounds in the mixed crystal have nearly identical shapes and orientations, thus accounting for the single crystal nature of the process. Finally, it was found that ketones lacking methyl substituents R to the benzoyl group are either photochemically unreactive or undergo Norrish type II cleavage. Possible reasons for this difference in behavior are presented and discussed.

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Section: Resultsmentioning

confidence: 89%

Section: Resultsmentioning

confidence: 99%