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Monday, December 27, 2010
Douglass F. Taber
University of Delaware

New Methods for Carbocyclic Construction: The Kim Synthesis of Pentalenene

Daesung Lee of the University of Illinois, Chicago, taking advantage of the facile insertion of an alkylidene carbene into a C-Si bond, established (J. Am. Chem. Soc. 2010, 132, 6640. ) a general method for the conversion of an α-silyl ketone 1 into the silyl cyclopropene 3. Christopher D. Bray of Queen Mary University showed (J. Org. Chem. 2010, 75, 4652. ) that the sulfonyl phosphonate 5 converted the enantiomerically-pure epoxide 4 into the cyclopropane 6. Paul Margaretha of the University of Hamburg observed (Org. Lett. 2010, 12, 728. ) smooth photochemical combination of 7 and 8 to give 9 with high diastereocontrol. Tőnis Kanger of the Tallinn University of Technology devised (Org. Lett. 2010, 12, 2230. ) the three-component coupling of 10, 11, and diethyl amine to give, after reduction, the highly-substituted cyclobutane 12.

Min Shi of the Shanghai Institute of Organic Chemistry uncovered (J. Org. Chem. 2010, 75, 902. ) an interesting new thermal rearrangement, the conversion of 13 to 14. José G. Ávila-Zárraga of the Universidad Nacional Autónoma de México applied (Tetrahedron Lett. 2010, 51, 2232. ) Pd catalysis to the cyclization of the epoxy nitrile 15, redirecting the reaction from the expected cyclobutane to the cyclopentanol 16. Ullrich Jahn of the Academy of Sciences of the Czech Republic effected (J. Org. Chem. 2010, 75, 4480. ) the oxidative radical cyclization of 17 to 18. Initial deprotonation of the substrate with t-BuMgCl switched the product to the trans diastereomer. Jonathan W. Burton of the University of Oxford employed (Org. Lett. 2010, 12, 2738. ) a related oxidative cyclization for the diastereoselective conversion of 19 to 20.

E. J. Corey of Harvard University reported (Org. Lett. 2010, 12, 300. ) a new ligand for the enantioselective Ni-mediated reduction of 21 to 22. Shu-Li You, also of the Shanghai Institute of Organic Chemistry, established (J. Am. Chem. Soc. 2010, 132, 4056. ) that the alcohol 23, readily prepared by oxidation of p-cresol, could be cyclized to the crystalline 25 in high ee. Seth B. Herzon of Yale University prepared (J. Am. Chem. Soc. 2010, 132, 2540. ) the crystalline enone 27, also in high ee, from the Birch reduction product 27. For related approaches to the enantioselective oxidation of benzene derivatives, see Chem. Commun. 2010, 701, and Org. Lett. 2010, 12, 2642, .

Manabu Node of Kyoto Pharmaceutical University optimized (J. Org. Chem. 2010, 75, 4201. ) an enantiomerically-pure amine for the cyclization of 28 to the highly-substituted cyclohexane 30. The chiral amine was easily removed and recycled by oxidation to the corresponding aldehyde.

Sunggak Kim, now at Nanyang Technical University, developed (Synlett 2010, 1511. ) the anionic chemistry of imines derived from N-amino diphenyl aziridine. He showed that addition of 3-butenyl lithium to 31 initiated a cascade cyclization. The tricyclic product 33 was readily converted to the sesquiterpene Pentalenene 34.

D. F. Taber, Org. Chem. Highlights 2010, December 27.
URL: http://www.organic-chemistry.org/Highlights/2010/27December.shtm