Organocatalytic C-C Ring Construction: Prostaglandin F_2α (Aggarwal)

Marco Lombardo of the Università degli Studi di Bologna devised (Adv. Synth. Catal. 2012, 354, 3428. DOI: 10.1002/adsc.201200922) a silyl-bridged hydroxyproline catalyst that mediated the enantioselective addition of 2 to cinnamaldehyde 1, to give 3. Yoann Coquerel and Jean Rodriguez of Aix Marseille Université showed (Adv. Synth. Catal. 2012, 354, 3523. DOI: 10.1002/adsc.201200658) that a hybrid epi-cinchonine catalyst directed the enantioselective and diastereoselective addition of the amide 4 to the nitro alkene 5, to give 6.

Magnus Rueping of RWTH Aachen observed (Angew. Chem. Int. Ed. 2012, 51, 12864. DOI: 10.1002/anie.201205813) that a chiral Brønsted acid mediated the diastereo- and enantioselective formation of 9 by the addition of 8 to cyclopentadiene 7. Marco Bandini, also of the University of Bologna, combined (Chem. Sci. 2012, 3, 2859. DOI: 10.1039/C2SC20478A) organocatalysis with gold catalysis to effect the cyclization of 10 to 11. Min Shi of the Shanghai Institute of Organic Chemistry prepared (Chem. Commun. 2012, 48, 2764. DOI: 10.1039/C2CC17709A) the quaternary cyclic amino acid derivative 14 by adding 13 to the acceptor 12.

Makoto Tokunaga of Kyushu University prepared (Org. Lett. 2012, 14, 6178. DOI: 10.1021/ol3027363) the ketone 17 by the hydrolytic enantioselective protonation of the enol ester 15. Hiyoshizo Kotsuki of Kochi University developed (Synlett 2012, 23, 2554. DOI: 10.1055/s-0032-1317317) a dual catalyst combination that effectively mediated the enantioselective addition of malonate even to the congested acceptor 18. Yoshitaka Hamashima and Toshiyuki Kan of the University of Shizuoka established (Org. Lett. 2012, 14, 6016. DOI: 10.1021/ol302908a) a protocol for the enantioselective brominative cyclization of 21, readily available by the reductive alkylation of benzoic acid.

Polycarbocyclic ring systems can also be prepared by organocatalysis. Ying-Chun Chen of Sichuan University tuned (J. Am. Chem. Soc. 2012, 134, 19942. DOI: 10.1021/ja3106219) cinchona-derived catalysts to selectively convert 23 into either endo (illustrated) or exo 25. Peng-Fei Xu, also of Lanzhou University, developed (Angew. Chem. Int. Ed. 2012, 51, 12339. DOI: 10.1002/anie.201206881) a supramolecular iminium catalyst for the intramolecular Diels-Alder cycloaddition of 26.

In a spectacular illustration of the power of organocatalysis, Varinder K. Aggarwal of the University of Bristol dimerized (Nature 2012, 489, 278. DOI: 10.1038/nature11411) succinaldehyde, from the hydrolysis of commercial 28, directly to the unsaturated aldehyde 29. Diastereoselective conjugate addition led to Prostaglandin F_2α 30.