Lewis acid mediated aldol condensations using thioester silyl ketene acetals |
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| Affiliation: | 1. Università degli Studi di Milano, Dipartimento di Chimica Organica e Industriale, Via Venezian 21, 20133 MilanoItaly;2. Università degli Studi di Milano, Dipartimento di Chimica Fisica ed Elettrochimica, Via Golgi 19, 20133 MilanoItaly;1. Institute of Neuroscience, Medical College, University of South China, Hengyang 421001, Hunan, PR China;2. Department of Neurology, Nanhua Affiliated Hospital, University of South China, Hengyang 421001, Hunan, PR China;3. Department of Pathophysiology, Medical College, University of South China, Hengyang 421001, Hunan, PR China;4. Hunan Province Cooperative innovation Center for Molecular Target New Drug Study, Hengyang 421001, Hunan, PR China;1. Institute of Research and Development, Duy Tan University, 03 Quang Trung, Da Nang, Viet Nam;2. Ivanovo State University of Chemistry and Technology, Sheremetievskiy Ave., 7, Ivanovo, 153000, Russian Federation;3. A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Division of the Russian Academy of Sciences, 1 Favorsky Street, 664033, Irkutsk, Russian Federation;1. Chittaranjan National Cancer Institute, Department of Cancer Chemoprevention, 37, S.P. Mukherjee Road, Kolkata 700 026, West Bengal, India;2. Chittaranjan National Cancer Institute, Department of Translational Research, 37, S.P. Mukherjee Road, Kolkata 700 026, West Bengal, India;1. Department of Imaging System Engineering, Pukyong National University, Busan 608-737, Republic of Korea;2. Chemistry Laboratory, College of Engineering, Kyungil University, Hayang 712-701, Republic of Korea;3. Department of Physics, Institute of Basic Sciences, Sungkyunkwan University, Suwon 440-746, Republic of Korea |
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| Abstract: | BF3-OEt2 mediated thioester silylketene acetal additions to aldehydes are stereoconvergent and give high anti-syn ratios and good chemical yields. An acyclic transition state model was hypothesized in order to account for the observed selectivity. Theoretical methods (MNDO) were used to evaluate the ground-state conformations of thioester silylketene acetals and to model the acyclic transition states. Lewis acid mediated additions of thioester silylketene acetals to 2-phenylpropion-aldehyde (BF3-OEt2), O-benzyl lactic aldehyde (SnCl4), 2,3-0,O-dibenzyl glyceraldehyde (SnCl4), and 3-benzyloxy-2-methylpropionaldehyde (TiCl4) were found to be highly diastereoface selective so that three contiguous stereocenters could be established. With α-, β- , or α,β-alkoxy aldehydes, relative stereoselection (chelation) effectively controls internal stereolection. The ground state conformations of the chiral aldehydes were studied using molecular mechanics (MM2). |
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