Construction of Stereochemical Arrays

The unprecedented enantioselective 1,8-addition of azlactone 1 to acylpyrrole 2 catalyzed by triaminophosphorane 3 was reported (J. Am. Chem. Soc. 2012, 134, 19370. DOI: 10.1021/ja310209g) by Takashi Ooi at Nagoya University. Tomislav Rovis at Colorado State University developed (Angew. Chem. Int. Ed. 2012, 51, 12330. DOI: 10.1002/anie.201206490) the asymmetric oxidative hetero-Diels-Alder reaction of propionaldehyde (5) and ketone 6 to produce lactone 8, catalyzed by NHC catalyst 7 in the presence of phenazine. A related NHC catalyst 11 was utilized (Angew. Chem. Int. Ed. 2012, 51, 8276. DOI: 10.1002/anie.201203449) by Xue-Wei Liu at Nanyang Technological University for the homoenolate addition of enal 9 to nitrodiene 10 to furnish 12 with high ee. The vinylogous conjugate addition of butenolide 13 to 15 to produce 16 with exquisite stereoselectivity was accomplished (Angew. Chem. Int. Ed. 2012, 51, 10069. DOI: 10.1002/anie.201205872) by Kuo-Wei Huang at KAUST, Choon-Hong Tan at Henan University and Nanyang Technological University, and Zhiyong Jiang at Henan University.

The enantioselective production of lactone 18 was achieved (J. Am. Chem. Soc. 2012, 134, 20197. DOI: 10.1021/ja3102709) by Jeffrey S. Johnson at the University of North Carolina at Chapel Hill by dynamic kinetic resolution (DKR) of α-keto ester 17. A related DKR strategy was employed (Org. Lett. 2012, 14, 6334. DOI: 10.1021/ol303115v) by Brinton Seashore-Ludlow at the KTH Royal Institute of Technology and Peter Somfai at Lund University in Sweden and the University of Tartu in Estonia for hydrogenation of α-amino-β-ketoester 19 to furnish aminoalcohol 21 with high ee.

Shigeki Matsunaga and Motomu Kanai at the University of Tokyo developed (Angew. Chem. Int. Ed. 2012, 51, 10275. DOI: 10.1002/anie.201205680) a unique strategy for the selective production of the cross-aldol adduct 24 by in situ generation of an aldehyde enolate from allyloxyborane 23 under rhodium catalysis. The highly diastereoselective construction of adduct 26 bearing two adjacent quaternary stereocenters by ketone allylation with allyl sulfide 25 was reported (Angew. Chem. Int. Ed. 2012, 51, 7263. DOI: 10.1002/anie.201202808) by Takeshi Takeda at the Tokyo University of Agriculture and Technology.

Wen-Hao Hu at East China Normal University reported (Nat. Chem. 2012, 4, 733. DOI: 10.1038/nchem.1406) the enantioselective three-component coupling of diazoester 27, N-benzylindole (28), and imine 29 to furnish 31 under the action of Rh₂(OAc)₄ and phosphoric acid 30. An alternative three-component coupling of diazophosphonate 32, o-methylaniline, and p-nitrobenzaldehyde to produce 33 was developed (Angew. Chem. Int. Ed. 2012, 51, 11376. DOI: 10.1002/anie.201206551) by Chi-Ming Che at the Shanghai Institute of Organic Chemistry.

Larry E. Overman at the University of California at Irvine found (Angew. Chem. Int. Ed. 2012, 51, 9576. DOI: 10.1002/anie.201204977) that the tertiary radical generated from N-(acyloxy)phthalimide 34 under visible light photoredox conditions underwent stereoselective conjugate addition to cyclopentenone 35 to produce 36, which is epimeric at C8 to the product obtained from cuprate addition. The domino carbopalladation-cross-coupling of amide 37 to produce 38 was reported (Org. Lett. 2012, 14, 3858. DOI: 10.1021/ol301539p) by Prof. Somfai.

Finally, Keith A. Woerpel at New York University reported (J. Am. Chem. Soc. 2012, 134, 12482. DOI: 10.1021/ja305713v) an exceedingly rare preparation of a seven-membered trans-alkene 42, via silyene transfer from 40 to diene 39 to furnish 41, followed by insertion of benzaldehyde. Although observable, 42 undergoes [1,3]-sigmatropic rearrangement to the oxasilacyclopentane 43 over several hours at ambient temperature.