Type A zwitterions and cyclohexadienone photochemical rearrangements. Mechanistic and exploratory organic photochemistry

Abstract

mL of benzene was added 0.40 mL of a 0.1 M solution of potassium tert-butoxide in tert-butyl alcohol. The mixture was stirred for 5 min at room temperature, diluted with ether, washed with saturated aqueous ammonium chloride, water, and brine, dried, and concentrated in vacuo to give 26 mg of a yellow solid. The material was subjected to preparative high-pressure LC using a 50 cm X 0.8 cm column packed with -20-µ porous silica beads.44 Elution with 35% ether in hexane at a flow rate of 4.8 mL/min gave two bands: band 1, retention time 11 min, 13 mg (48%) of 4-cyano-6,6-diphenylbicyclo[3.1.0]hex-3-en-2-one as faint yellow microcrystals, mp 178-179 °C; band 2, retention time 15 min, 11 mg (45%) of starting monobromo ketone. No 1-cyano-4-bromo-6,6-diphenylbicyclo [3.1.0] hexan-3-one (retention time 21 min) was observed.Control Experiment. Treatment of l-Cyano-6,6-diphenylbicyclo[3.1.0]hexan-3-one with Potassium tert-Butoxide. To a solution of 18 mg (0.066 mmol) of the 3-oxobicyclic compound in 4 mL of tert-butyl alcohol and 1 mL of benzene was added 0.66 mL of a 0.1 M solution of potassium tert-butoxide in tert-butyl alcohol. The mixture was stirred for 5 min at room temperature, diluted with ether, washed with saturated aqueous ammonium chloride, water, and brine, dried, and concentrated in vacuo to give 18 mg of a colorless oil. NMR analysis indicated pure starting ketone.Control Experiment. Treatment of 5-Cyano-6,6-diphenylbicyclo[3.1.0]hex-3-en-2-one with Potassium tert-Butoxide. To a solution of 27 mg (0.1 mmol) of the 5-cyano enone in 4.0 mL of tert-butyl alcohol and 1.0 mL of benzene was added 1.0 mL of a 0.1 M solution of potassium tert-butoxide in tert-butyl alcohol. The mixture was stirred for 5 min at room temperature, diluted with ether, washed with saturated aqueous ammonium chloride, water, and brine, dried, and concentrated in vacuo to give 27 mg of a white solid. NMR analysis indicated pure starting enone.Emission Measurements. Phosphorescence measurements were made on an Aminco-Kiers spectrophosphorimeter equipped with a Hanovia 901C-1,150-W, xenon arc lamp and modified with internal baffles to eliminate scatter. The spectra were obtained at 77 K in ethanol-ether (2:1) with the samples being thoroughly degassed immediately before measurements were made. The emission spectra were calibrated by use of a low-pressure mercury lamp in each run.

Divergent Photocyclization/1,4-Sigmatropic Rearrangements for the Synthesis of Sesquiterpenoid Derivatives

“…16 The uM06-2X functional has been used previously by Houk and co-workers to describe the triplet PES of the di-methane rearrangement of dibenzobarrelenes, and gives comparable results to multi-configurational (MCSCF) calculations. 17 In accord with Zimmerman's seminal experimental findings, 18 C3-C5 bond formation in triplet states of cycloheaxadienones 11 and 12 is facile (barriers of 3.6 and 6.1 kcal/mol, respectively). Recent MCSCF computations on the santonin-lumisantonin rearrangement show that intersystem crossing (ISC) to the singlet state can occur either at this stage, or following subsequent C-C cleavage.…”

“…The 6methyl-and 6-cyano-substituents formed the respective derivatives of 16, containing adjacent chiral quaternary centers, in good yield using visible light (entries 16, 17). Upon switching the solvent to acetonitrile, 15 could be observed in the course of the irradiation with visible light however, the ratio of 15:16 decreased until only 16 remained after full conversion of starting material (entries [18][19][20]. Similar results are obtained using UV-A and UV-B requiring significantly shorter reaction times (entries 21-23) while UV-C was optimal for obtaining 15 (entries 24-26).…”

Activity‐Directed Synthesis with Intermolecular Reactions: Development of a Fragment into a Range of Androgen Receptor Agonists

“…Rather than acting as co-substrates,these additives steered the reaction towards the rearranged product (9) [16,17] of an intramolecular C À H insertion:These reactions were discovered because product 9 is apotent partial agonist.…”

Activity‐Directed Synthesis with Intermolecular Reactions: Development of a Fragment into a Range of Androgen Receptor Agonists

“…Interestingly, with substrate 5 , the introduction of indole ( 6 f ) or 7-azaindole ( 6 n ) changed the outcome of the reaction. Rather than acting as co-substrates, these additives steered the reaction towards the rearranged product ( 9 )[ 16 , 17 ] of an intramolecular C–H insertion: These reactions were discovered because product 9 is a potent partial agonist.…”