C-N Ring Construction: The Hattori Synthesis of (+)-Spectaline
Magnus Rueping of RWTH Aachen University found (Chem. Commun. 2015, 51, 2111. DOI: 10.1039/C4CC09337B) that under Fe catalysis, a Grignard reagent would couple with the iodoazetidine 1 to give the substituted azetidine 2. Timothy F. Jamison of MIT established (Chem. Eur. J. 2015, 21, 7379. DOI: 10.1002/chem.201500886) a protocol for converting 3, readily available from commercial homoserine lactone, to the alkylated azetidine 4.
Long-Wu Ye of Xiamen University used (Chem. Commun. 2015, 51, 2126. DOI: 10.1039/C4CC09245G) a gold catalyst to cyclize 5, readily prepared in high ee, to the versatile ene sulfonamide 6. Chang-Hua Ding and Xue-Long Hou of the Shanghai Institute of Organic Chemistry added (Angew. Chem. Int. Ed. 2015, 54, 1604. DOI: 10.1002/anie.201409467) the racemic aziridine 7 to the enone 8 to give the pyrrolidine 9 in high ee. Arumugam Sudalai of the National Chemical Laboratory employed (J. Org. Chem. 2015, 80, 2024. DOI: 10.1021/jo5028886) proline as an organocatalyst to mediate the addition of 11 to 10, leading to the pyrrolidine 12. Aaron D. Sadow of Iowa State University developed (J. Am. Chem. Soc. 2015, 137, 425. DOI: 10.1021/ja511250m) a Zr catalyst for the enantioselective cyclization of the prochiral 13 to 14.
Masahiro Murakami of Kyoto University devised (Angew. Chem. Int. Ed. 2015, 54, 7418. DOI: 10.1002/anie.201502584) a Rh catalyst for the enantioselective ring expansion of the photocyclization product of 15 to the enamine 16. Sebastian Stecko and Bartlomiej Furman of the Polish Academy of Sciences reduced (J. Org. Chem. 2015, 80, 3621. DOI: 10.1021/acs.joc.5b00335) the carbohydrate-derived lactam 17 with the Schwartz reagent to give an intermediate that could be coupled with an isonitrile, leading to the amide 18. Lei Liu of Shandong University oxidized (Angew. Chem. Int. Ed. 2015, 54, 6012. DOI: 10.1002/anie.201500703) the alkene 19 in the presence of 20 to give 21. Tomislav Rovis of Colorado State University optimized (J. Am. Chem. Soc. 2015, 137, 4445. DOI: 10.1021/jacs.5b00033) a Zn catalyst for the addition of 22 to the nitro alkene 23, leading, after reduction, to the piperidine 24.
Carlos del Pozo and Santos Fustero of the Universidad de Valencia used (Org. Lett. 2015, 17, 960. DOI: 10.1021/acs.orglett.5b00054) a chiral auxiliary to direct the cyclization of 25 to the bicyclic amine 26. In another illustration of the use of microwave irradation to activate amide bond rotation, G. Maayan of Technion showed (Org. Lett. 2015, 17, 2110. DOI: 10.1021/acs.orglett.5b00696) that 27 could be cyclized efficiently to the medium ring lactam 28.
The alkaloid (+)-Spectaline (31) was isolated from the leaves of Cassia spectabilis. Yasunao Hattori of the Kyoto Pharmaceutical University constructed (Heterocycles 2015, 91, 959. DOI: 10.3987/COM-15-13172) the piperidine ring of 31 by the diastereoselective Pd-catalyzed cyclization of 29 to 30.