Resolution and Absolute Configurational Assignments to 1-Oxa- and 1-Thia-6-ketospiro[4.4]nonanyl Platforms
作者:Leo A. Paquette、James C. Lanter、Dafydd R. Owen、Fabrizio Fabris、Richard Todd Bibart、Miriam Alvarez
DOI:10.3987/com-00-s(i)8
日期:——
Analysis of the Conformational Nature, Resolvability, and Thermal Racemization of Hetero 2,3-Dispiro Cyclohexanones. The Weighting of Carbonyl/C-X Stabilization Relative to the Electronic Interaction between the Vicinal Electronegative Substituents
作者:Leo A. Paquette、Bruce M. Branan、Dirk Friedrich、Scott D. Edmondson、Robin D. Rogers
DOI:10.1021/ja00081a010
日期:1994.1
A series of hetero 2,3-dispiro cyclohexanones has been prepared. The conformations of the syn and anti isomers were assessed in the solid state, in solution, and in the gas phase (the latter by molecular mechanics calculations). The results are discussed in the light of steric, dipole, and gauche interactions; steric contributions give evidence of controlling DELTAG(eq). On a different front, the syn/anti pairs were found to interconvert when heated in the presence of a catalytic amount of acid. Three representative examples of these chiral molecules were resolved and complete racemization was observed to result under the conditions of equilibration. A push-pull fragmentation of the cyclohexanone ring is proposed to account for these observations, with the tethered oniom ion-enol pair reclosing to reconstitute the original, although stereochemically scrambled, structure. The intervention of the thionium ion intermediates is less thermodynamically favorable than that of oxonium ions, as expected.
Paquette Leo A., Branan Bruce M., Friedrich Dirk, Edmondson Scott D., Rog+, J. Amer. Chem. Soc, 116 (1994) N 2, S 506-513
作者:Paquette Leo A., Branan Bruce M., Friedrich Dirk, Edmondson Scott D., Rog+
DOI:——
日期:——
Studies of π-diastereofacial selectivity: Spiro 2-tetrahydrofuran and 2-tetrahydrothiophene ketones
作者:Martin Dimitroff、Alex G Fallis
DOI:10.1016/s0040-4039(98)00407-9
日期:1998.4
The facial influence and synthetic utility of oxygen, sulfur and carbon atoms adjacent to the ketone in the series of alpha-spiro ketones 2, 3, and 4 upon nucleophilic addition has been examined. Addition to the carbonyl group displayed a preference for attack anti to the heteroatom in competition with carbon in synthetically useful ratios. Hydride reduction of 2 with chelating reagents (NaBH4, LiAlH4 etc.) reversed this facial preference. (C) 1998 Elsevier Science Ltd. All rights reserved.
C4‘-Spiroalkylated Nucleosides Having Sulfur Incorporated at the Apex Position
作者:Leo A. Paquette、Fabrizio Fabris、Fabrice Gallou、Shuzhi Dong
DOI:10.1021/jo030196w
日期:2003.10.1
Methodology based on the concept of thionium ion-initiated pinacolic ring expansion has been developed for accessing C4'-spirocyclic thionucleosides. The readily available racemic ketones 6 and 37 are conveniently resolved via their acetals with (R)-mandelic acid. Subsequent reactions beginning with utilization of the Pummerer rearrangement lend themselves to functionalization of the spirocyclic core