Stereoselective C-N Ring Construction
Ryoichi Kuwano of Kyushu University showed (J. Am. Chem. Soc. 2008, 130, 808. ) that diastereomerically and enantiomerically pure pyrollidines such as 2 could be prepared by hydrogenation of the corresponding pyrrole. Victor S. Martín of Universidad de la Laguna found (Org. Lett. 2008, 10, 2349. ) that the stereochemical outcome of the pyrrolidine-forming Nicholas cyclization could be directed by the protecting group on the N. Jianbo Wang of Peking University established (J. Org. Chem. 2008, 73, 1971. ) a convenient route to diazo esters such as 6. N-H insertion led to the pyrrolidine, which Zhen-Jiang Xu of the Shanghai Institute of Organic Chemistry and Chi-Ming Che of the University of Hong Kong showed (Org. Lett. 2008, 10, 1529. ) could be reduced with high diastereoselectivity to the hydroxy ester 7. Alternatively, Professor Wang found that photochemical Wolff rearrangement of 6 delivered the pyrrolidone 8. Martin J. Slater and Shiping Xie of GlaxoSmithKline optimized (J. Org. Chem. 2008, 73, 3094. ) the hydroquinine catalyzed enantioselective 3+2 cycloaddition of 9 and 10, leading to the pyrrolidine 11 with high diastereocontrol.
Shu Kobayashi of the University of Tokyo developed (Adv. Synth. Catal. 2008, 350, 647. ) a practical protocol for the aza Diels-Alder construction of enantiomerically-pure piperidines such as 14. Biao Yu of the Shanghai Institute of Organic Chemistry cyclized (Tetrahedron Lett. 2008, 49, 672. ) the product from the proline-catalyzed enantioselective aldol of 15 and 16, leading to the substituted piperidine 17. Michael Shipman of the University of Warwick described (Tetrahedron Lett. 2008, 49, 250. ) the cyclization of the aziridine derived from 18, that proceeded to give 19 as a single diastereomer, apparently via kinetic side-chain protonation.
Takeo Kawabata of Kyoto University found (J. Am. Chem. Soc. 2008, 130, 4153. ) that intramolecular alkylation to form four, five and six-membered rings from amino esters such as 21 proceeded with remarkable enantioretention.
Géraldine Masson and Jieping Zhu of CNRS, Gif-sur-Yvette, condensed (Org. Lett. 2008, 10, 1509. ) cinnamaldehyde (23) with cyanide and an ω-alkenyl amine to give the intramolecular aza-Diels-Alder substrate 24. Hongbin Zhai of the Shanghai Institute of Organic Chemistry acylated (J. Org. Chem. 2008, 73, 3589. ) 26 with 27, leading to the ring-closing metathesis precursor 28. Tomislav Rovis of Colorado State University developed (Org. Lett. 2008, 10, 1231. ) the Rh-catalyzed condensation of the isocyanate 30 with alkyl alkynes to give 31, and with aryl alkynes to give 32.