Reduction in Organic Synthesis: The Miyaoka Synthesis of Sinularianin B
Alexander T. Radosevich of Pennsylvania State University devised (J. Am. Chem. Soc. 2015, 137, 5292. DOI: 10.1021/jacs.5b01899) a protocol for reducing an allylic bromide 1 to the transposed alkene 2. Kin Shing Chan of the Chinese University of Hong Kong found (Tetrahedron Lett. 2015, 56, 2728. DOI: 10.1016/j.tetlet.2015.04.014) that Co porphyrin catalyzed the reduction of an aryl bromide 3 to anisole 4. Nasser Iranpoor of Shiraz University activated (Org. Lett. 2015, 17, 214. DOI: 10.1021/ol503560e) the phenol 5 with 2,4,6-trichloro-1,3,5-triazine, then directly reduced that product to give 6. Axel Jacobi von Wangelin of the University of Regensburg prepared (Chem. Eur. J. 2015, 21, 4518. DOI: 10.1002/chem.201406461) anisole 4 by removing the diazo group of 7, by irradiation with green LED’s in the presence of eosin B.
Andreas Gansäuer of the Universität Bonn selectively reduced (Angew. Chem. Int. Ed. 2015, 54, 6931. DOI: 10.1002/anie.201501729) the epoxy alcohol 8 to the diol 9. Yuanhong Liu of the Shanghai Institute of Organic Chemistry showed (Chem. Commun. 2015, 51, 6426. DOI: 10.1039/C5CC00950B) that the propargylic amine 10 could be reduced to the Z alkene 11. Mark J. Coster of Griffith University used (Tetrahedron Lett. 2015, 56, 2059. DOI: 10.1016/j.tetlet.2015.03.008) the borane-dimethyl sulfide complex to reduce the N-acyl sulfonamide 12 to the alkyl sulfonamide 13. Sukbok Chang of the Korea Advanced Institute of Science and Technology effected (Angew. Chem. Int. Ed. 2015, 54, 6832. DOI: 10.1002/anie.201502366) proximal hydrosilylation of the unsaturated nitrile 14 to give, after reduction of the nitrile, protection of the resulting amine, and oxidation of the carbon-silicon bond, the hydroxy sulfonamide 15.
Hans Adolfsson of Stockholm University developed (Org. Lett. 2015, 17, 446. DOI: 10.1021/ol503430t) the polymeric silane PMHS as a mild reagent for the reduction of an amide 16 to the amine 17. Dmitry G. Gusev of the Wilfrid Laurier University prepared (J. Am. Chem. Soc. 2015, 137, 3743. DOI: 10.1021/ja512389y) an Os complex that selectively mediated the hydrogenation of the ester 18 to the alcohol 19, leaving the very reactive alkene intact. Norio Sakai of the Tokyo University of Science demonstrated (Eur. J. Org. Chem. 2015, 1591. DOI: 10.1002/ejoc.201403539) that an ester 20 could be converted directly to the iodide 21. In another application of reduction mediated by visible light, Carl-Johan Wallentin of Gothenburg University effected (Org. Lett. 2014, 16, 4228. DOI: 10.1021/ol5019294) decarboxylation of the α-amino acid 22 to 23.
In the course of a synthesis (Heterocycles 2015, 90, 442. DOI: 10.3987/COM-14-S(K)42) of Sinularian B (26), a valerane sesquiterpene isolated from the Formosan soft coral Sinularia sp., Hiroaki Miyaoka of the Tokyo University of Pharmacy and Life Sciences reductively removed the sulfone from 24 to give the desired diastereomer 25. This reduction is very likely proceeding by way of the intermediate π-allyl Pd complex.