Heterocycle Construction: The Koo Synthesis of (-)-Hanishin
Beeriah Baire of the Indian Institute of Technology Madras rearranged (J. Org. Chem. 2015, 80, 8314. DOI: 10.1021/acs.joc.5b01420) the acetylenic aldehyde 1 to the furan 2 by exposure to acid. Ronald J. Rahaim of Oklahoma State University added (Tetrahedron Lett. 2015, 56, 5738. DOI: 10.1016/j.tetlet.2015.09.021) the intermediate organometallic from the combination of 3 and 4 to the aldehyde 5, leading to the furan 6.
Chandan K. Jana of the Indian Institute of Technology Guwahati showed (Org. Lett. 2015, 17, 3762. DOI: 10.1021/acs.orglett.5b01744) that the addition of an excess of pyrrolidine 7 to the aldehyde 8 gave an intermediate that could be rearranged with strong base to the pyrrole 9. Wei Zeng of the South China University of Technology used (Chem. Commun. 2015, 51, 15328. DOI: 10.1039/C5CC06428G) a Rh catalyst to prepare the pyrrole 12 by combining the α-diazo ketone 11 with the imine 10. Naohiko Yoshikai of the Nanyang Technological University reported (Chem. Sci. 2015, 6, 6448. DOI: 10.1039/C5SC02322J) related results (not illustrated) using a Cu catalyst.
Sezgin Kiren of Winston Salem State University developed (Tetrahedron Lett. 2015, 56, 5275. DOI: 10.1016/j.tetlet.2015.07.045) a protocol for converting the dihydropyridone 13 to the pyridine 14. D. Tyler McQuade of Florida State University converted (J. Org. Chem. 2015, 80, 8583. DOI: 10.1021/acs.joc.5b01169) the propylidene malononitrile 15 to the pyridine 16. René Peters of the Universität Stuttgart added (J. Org. Chem. 2015, 80, 6822. DOI: 10.1021/acs.joc.5b01065) the isoxazolinone 17 to the enone 18 to assemble the pyridine 19. Zhi-Xiang Yu of Peking University and Jian Wang of Tsinghua University found (J. Am. Chem. Soc. 2015, 137, 9489. DOI: 10.1021/jacs.5b06400) that a Ru catalyst could mediate the selective preparation of the pyridine 21 by the combination of the enamide 20 with the alkyne 4.
Takanori Shibata of Waseda University effected (Chem. Eur. J. 2015, 21, 11340. DOI: 10.1002/chem.201502300) the regioselective cyclization of the α-amino ketone 22 to the indole 23. Bing Zhou of the Shanghai Institute of Materia Medica prepared (Angew. Chem. Int. Ed. 2015, 54, 15400. DOI: 10.1002/anie.201508702) the N-hydroxy indole 26 by combining the nitrone 24 with the diazo malonate 25, followed by hydrolysis. In Su Kim of Sungkyunkwan University described (Chem. Commun. 2015, 51, 17229. DOI: 10.1039/C5CC07767B) a related investigation leading to N-pyridyl indoles (not illustrated).
Fabio Ragaini of the University of Milano developed (Eur. J. Org. Chem. 2015, 5712. DOI: 10.1002/ejoc.201500933) the reductive cyclization of the nitro styrene 27 to the indole 28. Sreenivas Katukojvala of the Indian Institute of Science Education & Research assembled (Org. Lett. 2015, 17, 5878. DOI: 10.1021/acs.orglett.5b03064) the indole 31 by adding the pyridazine N-oxide 29 to the pyrrole 30.
The Maillard reaction of sugars with primary amines has long been known to form pyrroles, along with a variety of other products. En route to (-)-Hanishin (34), Sangho Koo of Myong Ji University made (J. Org. Chem. 2015, 80, 7693. DOI: 10.1021/acs.joc.5b01349) this a practical procedure, preparing 33 by combining 32 with the inexpensive ribose.