Regiospecific and Stereoselective Syntheses of (±)-Reserpine and (−)-Reserpine
作者:Gilbert Stork、Peng Cho Tang、Michael Casey、Burton Goodman、Masahiro Toyota
DOI:10.1021/ja055744x
日期:2005.11.23
Full details of three approaches to an entirely regio- and stereoselective synthesis of the well-known target reserpine are described, culminating in a totalsynthesis which efficiently meets these requirements.
Diastereoselective radical cyclization of bromoacetals (Ueno-Stork reaction) controlled by the acetal center
作者:Félix Villar、Philippe Renaud
DOI:10.1016/s0040-4039(98)01971-6
日期:1998.11
The stereochemistry of the 5-exo-trig cyclization of bromoacetals (Ueno-Stork cyclization) can be controlled from the stereogenic acetal center. High stereoselectivities have been observed for the formation of 4-substituted tetrahydrofurans. Preparation of an optically pure β-substituted γ-butyrolactone by use of an easily removable chiral auxiliary is reported.
Igbal, Javed; Srivastava, Rajeev Ranjan; Gupta, Kiran Bala, Synthetic Communications, 1989, vol. 19, # 5and6, p. 901 - 906
作者:Igbal, Javed、Srivastava, Rajeev Ranjan、Gupta, Kiran Bala、Khan, M. Amin
DOI:——
日期:——
Formation of Some Oxygen-Containing Heterocycles by Radical Cyclization: The Stereochemical Influence of Anomeric Effects
作者:Athelstan L. J. Beckwith、Dennis M. Page
DOI:10.1021/jo980359u
日期:1998.7.1
The influence of the anomeric effect on radical cyclization has been examined by determining the stereochemical outcome of the ring closure of 10 suitably substituted radicals. The stereochemistry of the products formed from the acyclic precursors 4a-f indicates that for suitably constituted radicals anomeric interactions stabilize pseudoaxially substituted transition structures 14 thus affording products with stereochemistry the reverse of that normally observed.
Generation and Mesolysis of PhSeSiR<sub>3</sub>]<sup>•-</sup>: Mechanistic Studies by Laser Flash Photolysis and Application for Bimolecular Group Transfer Radical Reactions
作者:Ganesh Pandey、K. S. Sesha Poleswara Rao、D. K. Palit、J. P. Mittal
DOI:10.1021/jo972345e
日期:1998.6.1
The investigation presented in this paper explores the mechanistic aspects and synthetic potentials of PET promoted reductive activation of selenosilane la to its radical anion la(-.). PET activation of la is achieved through a photosystem comprising a light-absorbing electron-rich aromatic (ERA), such as DMN or DMA, as an electron donor and ascorbic acid as a co-oxidant. The evidence for the ET from excited singlet states of DMN as well as DMA to la is suggested by estimating negative Delta G(et) (-51 and -43.46 kcal mol(-1), respectively) values and nearly diffusion-controlled fluorescence quenching rate constants (k(q)TR) 0.36 x 10(10) M-1 s(-1) and 0.28 x 10(10) M-1 s(-1), respectively, from time-resolved fluorescence quenching study. The transient absorption spectra of DMN.+, DMA(.+), and la(.-) are obtained initially by pulse radiolysis in order to correlate the time-resolved absorption spectral data. Laser flash photolysis studies in the nanosecond time domain have confirmed the generation of la(.-), DMN.+, and DMA(.+), supporting the participation of the triplet state of DMN or DMA in the ET reaction. Mesolytic cleavage of 1a(.-) produced a silyl radical and a phenyl selenide anion. The preparative PET activation of la in acetonitrile in the presence of DMN or DMA leads to the formation of 5 and 6, confirming the fragmentation pattern of la(.-). The overall ET rate constants (K-r(DMN) = 0.99 x 10(10) M-1 s(-1) and k(r)(DMA) = 1.62 x 10(10) M-1 s(-1)) and limiting quantum yields (phi(lim)DMN) = 0.034 and phi(lim)(DMA) = 0.12) are estimated from the inverse plot (1/[la] vs 1/phi(dis)) Obtained by measuring the dependence of photodissociation quantum yields of la at its maximum concentration in the presence of DMN or DMA. Silicon-centered radical species generated from the mesolysis of la(.-) are utilized for initiating a radical reaction by the abstraction of halogen atom from -C-X (X = Cl, Br) bonds, while PhSe- terminates the radical sequences via PhSeSePh. This concept is successfully applied for the bimolecular group transfer (BMGT) radical reactions and intermolecular radical chain addition reactions.