C-O Ring Construction: The Oger/Lee/Galano Synthesis of 7(RS)-ST-Δ⁸-11-dihomo-Isofuran

Shaorong Yang and Huanfeng Jiang of the South China University of Technology assembled (Angew. Chem. Int. Ed. 2014, 53, 7219. DOI: 10.1002/anie.201403341) the β-lactone 3 by the Pd-catalyzed addition of 2 to the alkyne 1. Jack R. Norton of Columbia University observed (J. Am. Chem. Soc. 2015, 137, 1036. DOI: 10.1021/ja511883b) that the vanadium-mediated reductive cyclization of 4 proceeded by a free radical mechanism, leading to the cis 3,4-disubstituted tetrahydrofuran 5. The cyclization of 6 to 7 developed (J. Org. Chem. 2015, 80, 965. DOI: 10.1021/jo502499a) by Glenn M. Sammis of the University of British Columbia also involved H atom transfer. Amy R. Howell of the University of Connecticut devised (J. Org. Chem. 2015, 80, 5196. DOI: 10.1021/acs.joc.5b00604) the ring expansion of the β-lactone 8 to the tetrahydrofuran 9. Dmitri V. Filippov and Jeroen D. C. Codée of Leiden University showed (J. Org. Chem. 2015, 80, 4553. DOI: 10.1021/acs.joc.5b00419) that the net reductive alkylation of the lactone 10 led to 11 with high diastereocontrol.

A. Stephen K. Hashmi of the Ruprecht-Karls-Universität Heidelberg optimized (Chem. Eur. J. 2015, 21, 427. DOI: 10.1002/chem.201402524) the gold-mediated rearrangement of the ester 12 to the lactone 13. This reaction apparently proceeded by the coupling of the metalated lactone with a propargylic carbocationic species.

Benjamin List of the Max-Planck-Institut für Kohlenforschung developed (Angew. Chem. Int. Ed. 2015, 54, 7703. DOI: 10.1002/anie.201500219) an organocatalyst that mediated the addition of 15 to 14, leading to 16 in high ee. Scott E. Denmark of the University of Illinois published (Nature Chem. 2015, 6, 1056. DOI: 10.1038/nchem.2109) a detailed study of the enantioselective cyclization of 17 to 18. Shunichi Hashimoto of Hokkaido University established (Tetrahedron Lett. 2015, 56, 1397. DOI: 10.1016/j.tetlet.2015.01.125) that his catalyst was effective for the cyclization of 19 to 20. Debendra K. Mohapatra of the Indian Institute of Chemical Technology showed (J. Org. Chem. 2015, 80, 1365. DOI: 10.1021/jo502101u) that allyl trimethylsilane could trap the intermediate from the cyclization of 21, leading to 22 with high diastereocontrol.

Younger-Suh of Seoul National University used (Chem. Commun. 2015, 51, 9026. DOI: 10.1039/C5CC02215K) a Pd catalyst to cyclize 23 to (-)-Deguelin (24). John Montgomery of the University of Michigan showed (Org. Lett. 2015, 17, 1493. DOI: 10.1021/acs.orglett.5b00381) that the Ni-catalyzed reductive cyclization of 25 to 26 proceeded with high diastereoselectivity.

The neurofurans and dihomoisofurans, exemplified by 7(RS)-ST-Δ⁸-dihomo-IsoF (29), are potential biomarkers of oxidative stress. Camille Oger and Jean-Marie Galano of Université de Montpellier and Jetty Chung-Yung Lee of the University of Hong Kong described (Chem. Eur. J. 2015, 21, 2442. DOI: 10.1002/chem.201405497) a general route to the isofurans and neurofurans, based on the Borhan cyclization of 27 to 28.