Tributylstannane → 2-((1S,3S)-3-hydroxy-4,4-dimethylcyclohexyl)isoindoline-1,3-dione

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Reaction Steps

A mixture of 2-((1R,2S,3S)-2-bromo-3-hydroxy-4,4-dimethylcyclohexyl)isoindoline-1,3-dione, 2-((1S,2R,3R)-2-bromo-3-hydroxy-4,4-dimethylcyclohexyl)isoindoline-1,3-dione, 2-((1R,2R,3R)-3-bromo-2-hydroxy-4,4-dimethylcyclohexyl)isoindoline-1,3-dione, and 2-((1S,2S,3S)-3-bromo-2-hydroxy-4,4-dimethylcyclohexyl)isoindoline-1,3-dione (5.7 g, 16.18 mmol) was dissolved in toluene (90 mL) and methanol (9 mL). To the solution was added tributyltin hydride (5.66 mL, 21.04 mmol) over 10 min via syringe under nitrogen, followed by azobisisobutyronitrile (0.266 g, 1.618 mmol) in one portion. The mixture was allowed to stir at reflux under a nitrogen atmosphere overnight. The reaction mixture was concentrated under reduced pressure to afford a residue that was purified by silica gel chromatography (0-50% ethyl acetate/hexane) yielding a mixture of 2-((1R,3R)-3-hydroxy-4,4-dimethylcyclohexyl)isoindoline-1,3-dione and 2-((1S,3S)-3-hydroxy-4,4-dimethylcyclohexyl)isoindoline-1,3-dione (0.9 g, 3.29 mmol, 20.35% yield). 1H NMR (400 MHz, DMSO-d6) δ ppm 7.82 (s, 4H), 4.51-4.80 (m, 1H), 3.80-4.03 (m, 2H), 2.84-3.11 (m, 1H), 1.49-1.67 (m, 3H), 1.37-1.47 (m, 1H), 1.22-1.35 (m, 1H), 1.13 (s, 3H), 0.80-0.93 (m, 3H). MS (ESI) m/z 274.0 [M+1]+. The regiochemistry of the product mixture was verified by small molecule X-ray crystal diffraction. The X-ray structure was solved as follows. The single crystal X-ray diffraction studies were carried out on a Bruker Kappa APEX-II CCD diffractometer equipped with Mo Kα radiation (λ=0.71073 Å). Crystals were grown by vapor diffusion of pentane into a DCM solution. A 0.25×0.20×0.05 mm colorless plate was mounted on a Cryoloop with Paratone oil. Data were collected in a nitrogen gas stream at 90(2) K using φ and ω scans. Crystal-to-detector distance was 60 mm and exposure time was 20 seconds per frame using a scan width of 0.5°. Data collection was 100% complete to 25.00° in θ. A total of 10827 reflections were collected covering the indices, −21<=h<=12, −7<=k<=8, −28<=l<=29. 2892 reflections were found to be symmetry independent, with a Rint of 0.0821. Indexing and unit cell refinement indicated a primitive, orthorhombic lattice. The space group was found to be Pbcn. The data were integrated using the Bruker SAINT software program and scaled using the SADABS software program. Solution by direct methods (SHELXS) produced a complete phasing model consistent with the proposed structure of a mixture of the enantiomeric pair 2-((1R,3R)-3-hydroxy-4,4-dimethylcyclohexyl)isoindoline-1,3-dione and 2-((1S,3S)-3-hydroxy-4,4-dimethylcyclohexyl)isoindoline-1,3-dione.

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