C-O Ring Construction: The Tong Synthesis of (-)-Aculeatin A
Oxetanes are both interesting structural elements and activated leaving groups. James A. Bull of Imperial College London cyclized (Chem. Commun. 2014, 50, 5203. ) the tosylate 1 to the oxetane with LiHMDS, then alkylated the product using the same base to give 2. J. S. Yadav of CSIR-Indian Institute of Chemical Technology established (Org. Lett. 2014, 16, 836. ) conditions for the cyclization of 3 to 4.
Hiroaki Sasai of Osaka University used (Chem. Commun. 2013, 49, 11124. ) a Pd(II)-Pd(IV) cycle to convert 5 to 6. Lauri Vares of the University of Tartu demonstrated (Tetrahedron Lett. 2014, 55, 3569. ) that the racemic epoxide 7, a mixture of diastereomers, could be cyclized to 8 as a single diastereomer in high ee. Alistair Boyer of the University of Glasgow converted (Org. Lett. 2014, 16, 1660. ) the triazole 9, prepared from the corresponding alkyne, to the intermediate 10, that could be hydrolyzed to the ketone or reduced to the amine. Subhas Chandra Roy of the Indian Association for the Cultivation of Science devised (Eur. J. Org. Chem. 2014, 2980. ) a Ti (III)-mediated cascade conjugate addition-cyclization for the assembly of 12 from 11.
Paul E. Floreancig of the University of Pittsburgh reported (Angew. Chem. Int. Ed. 2014, 53, 4926. ) the highly diastereoselective reductive cyclization of 13 to 14. Arun K. Ghosh of Purdue University prepared (J. Org. Chem. 2014, 79, 5697. ) the ketone 16 from the enantiomerically-pure alcohol 15. Professor Ghosh also described (Org. Lett. 2014, 16, 3154. ) a complementary approach to tetrahydropyrans based on the hetero Diels-Alder addition of the alkynyl aldehyde 18 to the diene 17. Xin-Shan Ye of Peking University found (J. Org. Chem. 2014, 79, 4676. ) that the alcohol 20 could be cyclized to 21 with NBS, and to the diastereomer with PhSeCl.
Jiyong Hong of Duke University showed (Org. Lett. 2014, 16, 2406. ) that an organocatalyst could be used to mediate the cyclization of 22 to the oxepane 23. Mingji Dai, also of Purdue University, reported (Angew. Chem. Int. Ed. 2014, 53, 6519. ) the carbonylative macrocyclization of the diol 25 to the lactone 25.
The Aculeatin family of natural products, isolated from the rhizomes of Amomum aculeatum that have long been used in Papua New Guinea to treat fever and malaria, indeed show potent in vitro activity against Plasmodium falciparum. Rongbiao Tong of the Hong Kong University of Science and Technology prepared (J. Org. Chem. 2014, 79, 1498. ) Aculeatin A (28) by the cyclization of 26 to 27, followed by selective reduction.