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[[alternative]]An Improved and Easy Method for the Preparation of 2,2-Disubstituted-1-Nitroalkenes

By [[author]]石裕國, Yuh-Kuo [[author]]Shih, 石裕國 and Yuh-Kuo Shih

Abstract

[[abstract]]PART 1 Ketones 1 and nitromethane 2 can react with the trapping reagents 6 (benzyl mercaptan 6a、thiophenol 6b或allyl mercaptan 6c) in the presence of catalytic amount of piperidine 3a to produce b-nitroalkyl sulfides (7, 10 or 11). By the use of CH2Cl2 as solvent and at 0 ℃, b-nitroalkyl sulfides (7, 10 or 11) can be oxidized by m-CPBA (m-chloroperoxybenzoic acid) 8a to produce b-nitroalkyl sulfoxides (9、12 or 13) and subsequently elimination to produce 2,2-disubstituted-1- nitroalkenes 5. The irreversibility of the synthetic mechanism not only could overcome the impracticability of the Henry reaction in the synthesis of 2,2-disubstituted-1-nitroalkenes 5 but also could produce the major product "exo-nitroolefins" 5f-h when cyclic ketones were used. By using this improved and easy methodology to prepare 2,2-disubstituted-1- nitroalkenes 5, medium to high yields of the products are observed. Compouds 5b and 5f-h also can be produced when b-nitroalkyl sulfoxides (9f、9g、12b、13f或13h) are treated with dilute aqueous basic solution, but the yields are lower than those under pyrolysis condition. PART 2 Reactions of ketones 1a-l, nitromethane 2 and benzyl mercaptan 6a in the presence of piperidine 3a or ethylenediamine 3b in tetrahydrofuran (THF) or acetonitrile (CH3CN) solution generate b-nitroalkyl sulfides 7a-l. By the use of 1,2-dichloroethane (ClCH2CH2Cl) as solvent, b-nitroalkyl sulfides 7a-l can be oxidized by m-chloroperoxybenzoic acid 8a, H2O2/AcOH 8b or H2O2 8c at 0 oC to generate b-nitroalkyl sulfoxides 9a-l first and then undergo elimination to produce medium to high yields of 2,2-disubstituted-1-nitroalkenes 5a-l under refluxing condition. One-pot synthesis of 5a-l from the reactions of 1a-l, 2, 3, and 6a in CH3CN solution under refluxing condition to generate 7a-l and then 7a-l was oxidized by 8a, 8b or 8c in the CH3CN and ClCH2CH2Cl solution at 0 oC to yield 9a-l. Finally, 9a-l undergo elimination under refluxing condition to yield expected products 5a-l with medium to high yields. The application of this one-pot methodology to prepare other 2,2-disubstituted-1-nitroalkenes 5m, 5n and 5o under similar conditions also get medium to high yields. Although this methodology can’t be applied to prepare nitroalkene from 1,4-cyclohexanedione 19, however, the unexpected product 20 can be observed under these conditions.

Topics: 硝基烯類, nitroalkene, [[classification]]39
Year: 2010
OAI identifier: oai:ir.lib.ntnu.edu.tw:309250000Q/2720
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