51787-73-6Relevant academic research and scientific papers
An Unexpected Product During Synthesis of 3-Phenylisoquinoline: Improved Preparation of 4-Hydroxy-3-phenylisoquinoline
Sard, Howard
, p. 1085 - 1088 (2007/10/02)
During repetition of the Bradsher procedure for the preparation of 3-phenylisoquinoline (1), an unexpected by-product was isolated, 4-hydroxy-3-phenylisoquinoline (3).This product is likely formed via allylic oxidation of a 1,4-dihydroisoquinoline interme
Benzyne-Oxazole Cycloadducts: Isolation and Retro-Diels-Alder Reactions
Whitney, Scott E.,Winters, Michael,Rickborn, Bruce
, p. 929 - 935 (2007/10/02)
A literature procedure for generating benzyne from 1-aminobenzotriazole and lead tetraacetate was modified by the use of two syringe pumps to effect simultaneous addition through opposing ports of a three-neck flask.Applied to the reaction of benzyne with 4-phenyloxazole at 0 deg C, this modification resulted in essentially quantitative formation of cycloadduct.Retro-Diels-Alder expulsion of benzonitrile with concurrent formation of isobenzofuran occurred when the adduct was heated.The sequence constitutes a useful method of preparation of isobenzofuran, which may be utilized in situ or isolated as a solution for subsequent application.Benzyne cycloadducts were also prepared from 4-(4-nitrophenyl)- and 4-(4-methoxyphenyl)oxazoles, in order to assess the effect of remote substituents on the retro-Diels-Alder reaction.First-order rate constants were determined at three temperatures in the range of 40-70 deg C.The order of reactivity was p-NO2 > p-H > p-OMe; the substituent effects were small, with a factor 4 separating the p-NO2 from p-OMe rate.All three substrates exhibited small ΔS(excit.) values.Expulsion of the nitrile is believed to occur as a concerted reaction with little charge development.The modified benzyne procedure was also applied to 2,5-diphenyloxazole, at 0 and -78 deg C.Oxazole was recovered (59percent and 43percent at the higher and lower temperature, respectively).No bis(benzyne) adduct was formed, showing that 1,3-diphenylisobenzofuran is not generated during the course of the reaction.The 1:1 benzyne-diphenyloxazole cycloadduct is not observed in the crude product of the0 deg C reaction, but an absorption at 6.09 ppm in the NMR spectrum of crude product from the -78 deg C reaction is attributed to this material.The latter crude product on standing at room temperature forms the isobenzofuran.Both reaction mixtures form 1,3-diphenylisobenzofuran by another mechanism involving a second intermediate.This more polar intermediate, which appears to be the major product at 0 deg C, slowly gives 1,3-diphenylisobenzofuran.The overall more efficient cycloaddition at - 78 deg C is attributed to entropy effects, which tend to favor Diels-Alder over other second-order reactions as the temperature is lowered.
Isolation of a 1:1 Oxazole-Benzyne Cycloadduct: An Improved Method for Generating Benzyne and a New Approach to Isobenzofuran
Whitney, Scott E.,Rickborn, Bruce
, p. 5595 - 5596 (2007/10/02)
A dual syringe pump addition procedure for benzyne generation from 1-aminobenzotriazole with Pb(OAc)4 is applied to 4-phenyloxazole at 0 deg C, to give the isolable 1:1 benzyne/oxazole Diels-Alder adduct in essentially quantitative yield; mild solution th
