C-O Ring Formation
The enantioselective bromocyclization of dicarbonyl 1 to form dihydrofuran 3 using thiocarbamate catalyst 2 was developed (Angew. Chem. Int. Ed. 2013, 52, 8597. DOI: 10.1002/anie.201304107) by Ying-Yeung Yeung at the National University of Singapore. Access to dihydrofuran 5 from the cyclic boronic acid 4 and salicylaldehyde via a morpholine-mediated Petasis borono-Mannich reaction was reported (Org. Lett. 2013, 15, 5944. DOI: 10.1021/ol402782f) by Xian-Jin Yang at East China University of Science and Technology and Jun Yang at the Shanghai Institute of Organic Chemistry. Chiral phosphoric acid 7 was shown (Angew. Chem. Int. Ed. 2013, 52, 13593. DOI: 10.1002/anie.201306801) by Jianwei Sun at the Hong Kong University of Science and Technology to catalyze the enantioselective acetalization of diol 6 to form tetrahydrofuran 8 with high stereoselectivity. Jan Deska at the University of Cologne reported (Org. Lett. 2013, 15, 5998. DOI: 10.1021/ol402887z) the conversion of glutarate ether 9 to enantiopure tetrahydrofuranone 10 by way of an enzymatic desymmetrization / oxonium ylide rearrangement sequence.
Perali Ramu Sridhar at the University of Hyderabad demonstrated (Org. Lett. 2013, 15, 4474. DOI: 10.1021/ol402021e) the ring-contraction of spirocyclopropane tetrahydropyran 11 to produce tetrahydrofuran 12. Michael A. Kerr at the University of Western Ontario reported (Org. Lett. 2013, 15, 4838. DOI: 10.1021/ol402252u) that cyclopropane hemimalonate 13 underwent conversion to vinylbutanolide 14 in the presence of LiCl and Me3N•HCl under microwave irradiation.
Eric M. Ferreira at Colorado State University developed (J. Am. Chem. Soc. 2013, 135, 17266. DOI: 10.1021/ja408957a) the platinum-catalyzed bisheterocyclization of alkyne diol 15 to furnish the bisheterocycle 16. Chiral sulfure ylides such as 17, which can be synthesized easily and cheaply, were shown (J. Am. Chem. Soc. 2013, 135, 11951. DOI: 10.1021/ja405073w) by Eoghan M. McGarrigle at the University of Bristol and University College Dublin and Varinder K. Aggarwal at the University of Bristol to stereoselectively epoxidize a variety of aldehydes.
The amine 20-catalyzed tandem heteroconjugate addition / Michael reaction of quinol 19 and cinnamaldehyde to produce bicycle 21 with very high ee was reported (Chem. Sci. 2013, 4, 2828. DOI: 10.1039/C3SC51022K) by Jeffrey S. Johnson at the University of North Carolina at Chapel Hill. Quinol ether 22 underwent facile photorearrangement-cycloaddition under irradiation, as reported (J. Am. Chem. Soc. 2013, 135, 17978. DOI: 10.1021/ja409992m) by John A. Porco, Jr. at Boston University and Corey R. J. Stephenson, now at the University of Michigan.
Scott D. Rychnovsky at the University of California at Irvine demonstrated (Org. Lett. 2013, 15, 4536. DOI: 10.1021/ol402095g) that reaction of hydroxysilyl enol ether 24 and aldehyde 25 in the presence of Lewis acid led to the formation of the tetrahydropyranone 26 as a single isomer. Chiral diamine catalyst 28 was found (ACS Catal. 2013, 3, 1356. DOI: 10.1021/cs4002332) by Gang Zou at East China University of Science and Technology and Gang Zhao at the Shanghai Institute of Organic Chemistry to catalyze the transformation of alcohol 27 to enantioenriched tetrahydrofuran 29 via heteroconjugate addition.
Decarboxylative allylation technology was employed (Angew. Chem. Int. Ed. 2013, 52, 5134. DOI: 10.1002/anie.201210266) by Xue-Wei Liu at Nanyang Technological University for the transformation of glycan 30 to dihydropyran 31 with complete stereoselectivity. Finally, Sanzhong Luo at the Institute of Chemistry, Chinese Academy of Sciences utilized (Angew. Chem. Int. Ed. 2013, 52, 9786. DOI: 10.1002/anie.201304561) the catalyst of combination of indium(III) salt and chiral phosphoric acid 33 to achieve the enantioselective cycloaddition of 32 and 1,5-hexadiene to produce the densely functionalized dihydropyran 34.