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403 results on '"Yao, Changsheng"'

3. Synthesis of α-chiral amides via synergistic visible-light-induced Wolff rearrangement and asymmetric NHC catalysis.

Author

Wang, Jiaomei, Chen, Yangxu, Miao, Siyan, Yao, Changsheng, and Zhang, Kai

Abstract

Herein, a visible-light-induced chiral N-heterocyclic carbene (NHC)-catalyzed asymmetric amination of ketenes has been developed. This strategy provides a convenient and facile synthetic protocol for the efficient construction of α-chiral amides under mild reaction conditions with moderate to excellent yields and stereoselectivities (up to 95% yields and 97 : 3 e.r.). Furthermore, a chiral 2-phenyl-1-propylamine derivative and (R)-ibuprofen could be obtained after simple transformations of the chiral products. [ABSTRACT FROM AUTHOR]

Published
2024
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16. Copper-catalyzed [3+2] annulation of O-acyl ketoximes with 2-aryl malonates for the synthesis of 3-aryl-4-pyrrolin-2-ones.

Author

Song, Xiao-Qing, Qiang, Xiao-Qi, Hu, Zi-Jun, Lyu, Xinyu, Tan, Sheng, Yao, Changsheng, Sun, Yong-Qiang, Miao, Chun-Bao, and Yang, Hai-Tao

Subjects
MALONATES, ENAMINES, OXIMES, OXIDIZING agents, ANNULATION
Abstract

A copper-catalyzed [3+2] annulation of O-acyl ketoximes with 2-aryl malonates for the concise synthesis of 3-aryl-4-pyrrolin-2-ones has been developed. The advantage of this method lies in the use of O-acyl oximes as an internal oxidant to generate the nucleophilic enamines and electrophilic p-quinone methides concurrently. The subsequent nucleophilic addition undergoes selectively on the α-C of malonates. [ABSTRACT FROM AUTHOR]

Published
2023
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40. DEP-TSPmeta: a multiple criteria Dynamic Ensemble Pruning technique ad-hoc for time series prediction.

Author

Zhang, Jing, Dai, Qun, and Yao, Changsheng

Abstract

Time series prediction (TSP) is a process of using data collected at different times in the past for statistical analysis, so as to speculate on the trend of things, where the non-stationary and non-linear characteristics of data portray a hard setting for predictive tasks. Obviously, there will be no single model that could perform the best for all TSP issues. Dynamic Ensemble Selection (DES) technique achieves more accurate and robust performance than a single model, due to that it aims to select an ensemble of the most competent models in a dynamic fashion according to each test sample. A variety of DES approaches have been proposed to address pattern classification problems, but little work has been conducted on the research of TSP adopting the DES paradigm. Commonly, the DES approaches work by the definition of a single criterion to evaluate the capability of base classifiers. However, only one criterion is often inadequate for the comprehensive evaluation of classifier power. Thus, in this paper, a multiple criteria Dynamic Ensemble Pruning (DEP) technique exploiting meta-learning ad-hoc for TSP, termed DEP-TSPmeta, based on the inspiration from a state-of-the-art META-DES framework specifically presented for classification tasks, is developed. Within DEP-TSPmeta, Extreme Learning Machines (ELMs) and Hierarchical Extreme Learning Machines (H-ELMs) are integrated as the base models, and four distinct meta-attributes collections, i.e., hard prediction, local accuracy, global accuracy, and prediction confidence, are presented. Each set of meta-attributes corresponds to a specific assessment criterion, i.e., the prediction accuracy in local area of the eigenspace, the overall local accuracy, the prediction accuracy in global area of the decision space, and the confidence level of predictor. A desirable meta-predictor, obtained by training on the strength of these meta-attributes, is the key to deciding whether a base predictor is capable of predicting the unseen instance well or not. Those incapable base predictors determined by the meta-predictor will be pruned and the capable predictors will be expanded into the final dynamic ensemble system. The size of the sets of meta-attributes is specified dynamically by genetic algorithm for different time series benchmark datasets. Empirical results on eight benchmark datasets with different time granularities have verified that, the proposed DEP-TSPmeta algorithm possesses dramatically improved prediction performance at different granularities, when compared against three other DES approaches and four static selective ensemble learning methods. [ABSTRACT FROM AUTHOR]

Published
2021
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