108817-72-7Relevant articles and documents
Boronic acid catalysis for mild and selective [3+2] dipolar cycloadditions to unsaturated carboxylic acids
Zheng, Hongchao,McDonald, Robert,Hall, Dennis G.
supporting information; experimental part, p. 5454 - 5460 (2010/09/15)
Herein, the concept of boronic acid catalysis (BAC) for the activation of unsaturated carboxylic acids is applied in several classic dipolar [3 + 2] cycloadditions involving azides, nitrile oxides, and nitrones as partners. These cycloadditions can be used to produce pharmaceutically interesting, small heterocyclic products, such as triazoles, isoxazoles, and isoxazolidines. These cycloadducts are formed directly and include a free carboxylic acid functionality that can be employed for fur-ther transformations, thereby avoiding prior masking or functionalization. In all cases, BAC provides faster reactions, under milder conditions, with much improved product yields and regioselectivities. In some instances, such as triazole formation from the reaction of azides with 2-alkynoic acids, catalysis with ort/io- nitrophenylboronic acid circumvents the undesirable product decarboxylation observed when using thermal activation. By using NMR spectroscopic studies, the boronic acid catalyst was shown to provide activation by a LUMO-lowering effect in the unsaturated carboxylic acid, likely via a monoacylated hemiboronic ester intermediate.
Cycloaddition of Nitrones with Allenes. An Example of Steric Control of Regiochemistry
Padwa, Albert,Kline, Donald N.,Koehler, Konrad F.,Matzinger, Michael,Venkatramanan, M. K.
, p. 3909 - 3917 (2007/10/02)
A study of the cycloaddition behavior of a series of electron-deficient allenes with C-phenyl-N-alkylnitrones has been carried out.The 1,3-dipolar cycloaddition proceeds in high yield with complete regiospecifity toproduce 5-methylene substituted isoxazol