- Making endo-cyclizations favorable again: A conceptually new synthetic approach to benzotriazoles via azide group directed lithiation/cyclization of 2-azidoaryl bromides
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Although benzotriazoles are important and ubiquitous, currently there is only one conceptual approach to their synthesis: bridging the two ortho-amino groups with an electrophilic nitrogen atom. Herein, we disclose a new practical alternative-the endo-cyclization of 2-azidoaryl lithiums obtained in situ from 2-azido-aryl bromides. The scope of the reaction is illustrated using twenty-four examples with a variety of alkyl, alkoxy, perfluoroalkyl, and halogen substituents. We found that the directing effect of the azide group allows selective metal-halogen exchange in aryl azides containing several bromine atoms. Furthermore, (2-bromophenyl)diazomethane undergoes similar cyclization to give an indazole. Thus, cyclizations of aryl lithiums containing an ortho-X = Y = Z group emerge as a new general approach for the synthesis of aromatic heterocycles. DFT computations suggested that the observed endo-selectivity applies to the anionic cyclizations of other functionalities that undergo "1,1-additions" (i.e., azides, diazo compounds, and isonitriles). In contrast, cyclizations with the heteroatomic functionalities that follow the "1,2-addition" pattern (cyanates, thiocyanates, isocyanates, isothiocyanates, and nitriles) prefer the exo-cyclization path. Hence, such reactions expand the current understanding of stereoelectronic factors in anionic cyclizations.
- Ageshina, Alexandra A.,Chesnokov, Gleb A.,Topchiy, Maxim A.,Alabugin, Igor V.,Nechaev, Mikhail S.,Asachenko, Andrey F.
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supporting information
p. 4523 - 4534
(2019/05/17)
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- Method for the control of stem growth and stem stiffness of graminaceous crops
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The invention is a novel method for the control of the relative stem growth of graminaceous crops, comprising applying to the foliage, stems, roots or seeds of said plants, or to the soil in which said plants are grown, a plant growth regulating amount of
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