Highly Diastereo- and Enantioselective Cu-Catalyzed [3 + 3] Cycloaddition of Propargyl Esters with Cyclic Enamines toward Chiral Bicyclo[<i>n</i>.3.1] Frameworks
作者:Cheng Zhang、Xin-Hu Hu、Ya-Hui Wang、Zhuo Zheng、Jie Xu、Xiang-Ping Hu
DOI:10.1021/ja303129s
日期:2012.6.13
Cu-catalyzed asymmetric [3 + 3] cycloaddition of propargyl esters with cyclic enamines is reported. With a combination of Cu(OAc)(2)·H(2)O and a chiral tridentate ferrocenyl-P,N,N ligand as the catalyst, perfect endo selectivities (endo/exo > 98/2) and excellent enantioselectivities (up to 98% ee) for endo cycloadducts were achieved under mild conditions. This method provides a simple and efficient approach
β,β‘- and α,β,β‘-Annulation Reactions of Cyclic Enamines: Enantioselective Synthesis of Bicyclo[3.<i>n</i>.1]alkenones (<i>n</i> = 2, 3) and Tricyclo[3.3.0.0<sup>2,8</sup>]octanes from Fischer Alkenyl Carbene Complexes
作者:José Barluenga、Alfredo Ballesteros、Javier Santamaría、Ramón Bernardo de la Rúa、Eduardo Rubio、Miguel Tomás
DOI:10.1021/ja002905i
日期:2000.12.1
Group 6 Heteroatom- and Non-Heteroatom-Stabilized Carbene Complexes. β,β‘- and α,β,β‘-Annulation Reactions of Cyclic Enamines
作者:José Barluenga、Alfredo Ballesteros、Ramón Bernardo de la Rúa、Javier Santamaría、Eduardo Rubio、Miguel Tomás
DOI:10.1021/ja0278077
日期:2003.2.19
Cyclization reactions of group 6 Fischer carbene complexes with cyclopentanone and cyclohexanone enamines are described. Enamine 3a undergoes thermal alpha,beta,beta'-annulation with alkenylcarbene complexes 1 and 2 (THF, 60degreesC), affording semibullvalenes 5. The metalate intermediates 6, resulting from beta,beta'-annulation of the enamines 3a and 4a, were quantitatively formed by running the reaction in hexane at room temperature. Acid-promoted demetalation of 6 afforded endo-2-bicyclo[3.2.1]octen-8-ones 7 and endolexo-2-bicyclo[3.3.1]nonen-9-ones 8 (endolexo = 5:1). Using (S)-methoxymethylpyrrolidine-derived enamines 3b and 4b,c allowed highly enantioenriched cycloadducts endo-(+)-7 as well as endo(-)-8 and exo-(-)-8 to be accessed. The non-heteroatom-stabilized carbene complex 10 was formed from complex 6 by Me3SiOTf-promoted elimination of the methoxy group, characterized by C-13 NMR, and transformed into the organic compounds 7, 7-d, and 11 as well as into bicyclo[3.2.1]octan-2,8-diones 14 and cycloheptanones 15. On the basis of this sequence, enantioenriched cycloheptanones (+)-15 were efficiently prepared in one pot from carbene complexes 2 and enamine 3b (51-55% yield, 91-96% ee). Extension of this work to simple Fischer carbene complexes 16 allowed an appropriate way to generate the nonstabilized pentacarbonyl[(phenyl(alkyl)carbene]tungsten complex 17 to be designed, for which the thermal and chemical behavior leading to compounds 18-21 is described.