Metal-Mediated C-C Ring Construction: (+)-Shiromool (Baran)
Seiji Iwasa of the Toyohashi University of Technology devised (Adv. Synth. Catal. 2012, 354, 3435. ) a water-soluble Ru catalyst for enantioselective intramolecular cyclopropanation that could be separated from the product and recycled by simple water/ether extraction. Minoru Isobe of the National Tsing Hua University combined (Org. Lett. 2012, 14, 5274. ) the Nicholas and Hosomi-Sakurai reactions to close the cyclobutane of 4.
Kazunori Koide of the University of Pittsburgh established (Tetrahedron Lett. 2012, 53, 6637. ) that the activity of a Ru metathesis catalyst, shut down by the presence of TBAF, could be restored by the inclusion of TMS2O. Jan Streuff of Albert-Ludwigs-Universität Freiburg demonstrated (Angew. Chem. Int. Ed. 2012, 51, 8661. ) that the enantiomerically-pure Brintzinger complex mediated the reductive cyclization of 7 to 8. Huw M. L. Davies of Emory University prepared (J. Am. Chem. Soc. 2012, 134, 18241. ) the cyclopentenone 11 by Rh-mediated addition of 10 to 9 followed by elimination. Christophe Meyer and Janine Cossy of ESPCI Paris showed (Angew. Chem. Int. Ed. 2012, 51, 11540. ) that the Rh-mediated rearrangement of 12 to 13 proceeded with substantial diastereocontrol.
Jian-Hua Xie and Qi-Lin Zhou of Nankai University observed (Org. Lett. 2012, 14, 6158. ) that the enantioselective hydrogenation of 14 followed by Claisen rearrangement established the cyclic quaternary center of 17 with high stereocontrol. Ken Tanaka of the Tokyo University of Agriculture and Technology devised (Angew. Chem. Int. Ed. 2012, 51, 13031. ) the Rh-mediated addition of the enyne 18 to 19 to give the highly-substituted cyclohexene 20. Daesung Lee of the University of Illinois at Chicago showed (Chem. Sci. 2012, 3, 3296. ) that the ring-opening/ring-closing metathesis of 21 delivered 22 with high diastereocontrol.
Andreas Speicher of Saarland University cyclized (Org. Lett. 2012, 14, 4548. ) 23 to 24 with significant atropisomeric induction. Erick M. Carreira of the Eidgenössische Technische Hochschule Zürich effected (J. Am. Chem. Soc. 2012, 134, 20276. ) the polycyclization of racemic 25 to 26 with high enantiomeric excess.
Medium rings are often the most dificult to construct, because of the inherent congestion across the forming ring. Philip S. Baran of Scripps/La Jolla effected (Angew. Chem. Int. Ed. 2012, 51, 11491. ) the cyclization of 27 to 28 as a single diastereomer. The epoxy alcohol 28 is a protean intermediate, convertible into a range both of natural products and of natural product-like substances, one of the simplest of which was (+)-Shiromool (29).