- Asymmetric Aza-Wacker-Type Cyclization of N-Ts Hydrazine-Tethered Tetrasubstituted Olefins: Synthesis of Pyrazolines Bearing One Quaternary or Two Vicinal Stereocenters
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We have developed an asymmetric aza-Wacker-type cyclization of N-Ts hydrazine-tethered tetrasubstituted olefins, affording optically active pyrazolines bearing chiral tetrasubstituted carbon stereocenters. This reaction is tolerant to a broad range of substrates under mild reaction conditions, giving the desired chiral products with high enantioselectivities. Generation of two vicinal stereocenters on the C=C double bonds was also achieved with high selectivities, a process which has been rarely studied for Wacker-type reactions. A mechanistic study revealed that this aza-Wacker-type cyclization undergoes a syn-aminopalladation process. It was also found that for substrates bearing two linear alkyl substituents on the outer carbon atom of the olefin, both of which are larger than a methyl group, the alkyl substituent that is cis to the intranucleophilic group participates more readily in β-hydride elimination. When one of the two alkyl substituents on the outer carbon atom of the olefin is a methyl group, β-hydride elimination proceeds selectively at the methylene side, thus both diastereomers can be prepared via switching the configuration of the olefin. Furthermore, the product can be converted to a pharmaceutical compound in high yields over three steps.
- Kou, Xuezhen,Shao, Qihang,Ye, Chenghao,Yang, Guoqiang,Zhang, Wanbin
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- A mild method for the replacement of a hydroxyl group by halogen: 3. the dichotomous behavior of α-haloenamines towards allylic and propargylic alcohols
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A study of the deoxyhalogenation of allylic and propargylic alcohols with tetramethyl-α-halo-enamines is reported. Primary allylic and primary and secondary propargylic alcohols gave the corresponding halides in high yields. Secondary allylic and propargylic alcohols yielded the corresponding secondary halides but the reaction also produced some rearranged primary halides (I > Br > Cl). The reactions with tertiary allylic and tertiary propargylic alcohols gave several products and was therefore of little synthetic value. However, the addition of triethylamine to the reaction mixture or the use of lithium alkoxide instead of alcohol brought about a major change of the course of the reaction which led to amides carrying an allyl or an allenyl group at C2. This was shown to result from a Claisen-Eschenmoser rearrangement of an intermediate α-allyloxy- or propargyloxy-enamine.
- Munyemana, Fran?ois,Patiny, Luc,Ghosez, Léon
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- Nickel-Catalyzed Asymmetric Reductive 1,2-Carboamination of Unactivated Alkenes
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Starting from diverse alkene-tethered aryl iodides and O-benzoyl-hydroxylamines, the enantioselective reductive cross-electrophilic 1,2-carboamination of unactivated alkenes was achieved using a chiral pyrox/nickel complex as the catalyst. This mild, modular, and practical protocol provides rapid access to a variety of β-chiral amines with an enantioenriched aryl-substituted quaternary carbon center in good yields and with excellent enantioselectivities. This process reveals a complementary regioselectivity when compared to Pd and Cu catalysis.
- He, Jun,Xue, Yuhang,Han, Bo,Zhang, Chunzhu,Wang, You,Zhu, Shaolin
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p. 2328 - 2332
(2020/01/08)
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- Method for preparing pentazocine intermediates
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The invention discloses a method for preparing pentazocine intermediates, and belongs to the field of medicine synthesis. The method includes synthesizing chiral intermediates by the aid of simple synthesis processes; carrying out addition and hydrogenation debenzylation to obtain key intermediates (-)-(2S, [2a, 6a, 11S])-1, 2, 3, 4, 5, 6-hexahydrogen-cis-6, 11-dimethyl-2, 6-methylene-3-benzo azocines-8-alcohol. The method has the advantages that the method is low in cost and high in yield and includes simple processes, and the chiral purity of the pentazocine intermediates which are productsprepared by the aid of the method can reach 98%.
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Paragraph 0033; 0034; 0035; 0045; 0046; 0047; 0054-0056
(2018/03/26)
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