- Ring-Strain Effects in Base-Induced Sommelet–Hauser Rearrangement: Application to Successive Stereocontrolled Transformations
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The base-induced Sommelet–Hauser (S–H) rearrangement of azetidine-2-carboxylic acid ester-derived ammonium salts into 2-aryl-substituted derivatives was demonstrated. The ring-strain of four-membered N-heterocycles enables efficient generation of the desired ylide intermediate and enhances the rate of the S–H rearrangement. The asymmetric version of the rearrangement was characterized by excellent levels of successive chirality transmissions. The regio- and stereo-controlled nucleophilic ring opening of the rearrangement products produced quaternary α-aryl amino acid esters with excellent enantiopurities.
- Tayama, Eiji,Watanabe, Kazutoshi,Matano, Yoshihiro
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p. 3631 - 3641
(2016/07/29)
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- Asymmetric α-2-tosylvinylation of in situ-generated N-2-tosylvinyl proline-derived ammonium ylides
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Asymmetric α-2-tosylvinylation of N-substituted proline esters using ethynyl tolyl sulfone as an electrophile was shown to proceed in good yield with high enantioselectivities without the addition of any bases. The reaction proceeds via the formation of N-2-tosylvinyl ammonium ylides.
- Igarashi, Tomohito,Tayama, Eiji,Iwamoto, Hajime,Hasegawa, Eietsu
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supporting information; experimental part
p. 1819 - 1821
(2011/05/05)
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- Iminium Salts from α-Amino Acid Decarbonylation. Application to the Synthesis of Octahydroindoloquinolizines
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Iminium salts, formed regiospecifically by the decarbonylation of tertiary α-amino acids, have been applied to the synthesis of substituted tetrahydro-β-carbolines.In this manner the octahydroindoloquinolizines 5-8 were prepared.Several useful methods for the synthesis of the requisite tertiary pipecolic acids 1-4 were developed.These include alkylation of secondary α-amino esters with tryptophyl bromide and alkylation of tryptophan methyl ester with α,ω-dibromo esters.Following deprotection, the resulting tertiary α-amino acids were heated in phenylphosphonic dichloride to give the cyclized products in good yield.The presence of other substituents α or β to the basic nitrogen induces stereoselectivity in the ring closure.When this substituent is an α-carboxylic acid, it can be replaced by hydrogen through decarbonaylation followed by reduction of the resulting iminium salt.
- Johansen, Jon E.,Christie, Bradley D.,Rapoport, Henry
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p. 4914 - 4920
(2007/10/02)
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