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Total Synthesis

Monday, November 17, 2008
Douglass F. Taber
University of Delaware

Stereoselective C-N Ring Construction

Ryoichi Kuwano of Kyushu University showed (J. Am. Chem. Soc. 2008, 130, 808. DOI: 10.1021/ja7102422) that diastereomerically and enantiomerically pure pyrrollidines 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. DOI: 10.1021/ol800544a) 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. DOI: 10.1021/jo702275a) 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. DOI: 10.1021/ol800087p) 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. DOI: 10.1021/jo800062c) 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. DOI: 10.1002/adsc.200700615) 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. DOI: 10.1016/j.tetlet.2007.11.153) 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. DOI: 10.1016/j.tetlet.2007.11.077) 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. DOI: 10.1021/ja077684w) 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. DOI: 10.1021/ol800199b) 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. DOI: 10.1021/jo8002425) 26 with 27, leading to the ring-closing metathesis precursor 28. Tomislav Rovis of Colorado State University developed (Org. Lett. 2008, 10, 1231. DOI: 10.1021/ol800086s) the Rh-catalyzed condensation of the isocyanate 30 with alkyl alkynes to give 31, and with aryl alkynes to give 32.

D. F. Taber, Org. Chem. Highlights 2008, November 17.