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481.
Christoffers J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(20):4862-4867
Extensive investigations of chiral auxiliaries and active metals for Michael addition of 1,3-dicarbonyl compounds with vinyl ketones are summarized. Our efforts result in a widely applicable auxiliary-mediated, copper(II) acetate-catalyzed procedure. For these purposes, L-valine diethylamide is an optimal chiral auxiliary giving quaternary stereocenters with up to 99 % ee at ambient temperature. No inert or anhydrous conditions are required, the solvent is simply acetone, and the auxiliary can be recovered almost quantitatively after workup. 相似文献
482.
Cleverson C. Bocca Roberto Rittner Alan P. da Silva Ernani A. Basso 《Journal of Physical Organic Chemistry》2011,24(3):241-248
Transition state (TS) structures for the reduction of 2‐Me and 2‐i‐Pr‐cyclohexanone by LiAlH4 were optimized by density functional theory (B3LYP/6‐31G(d,p)). Four TS structures corresponding to axial and equatorial attacks by LiAlH4 were located for each ketone conformer. Electronic potential maps were used to investigate the substituent electronic effect on the TS stabilization. The uneven carbonyl orbital distribution in the LUMO (π*) was also analyzed. Reduction stereoselectivity was shown to depend on both the ketone conformational ratio and on the reaction TS. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
483.
484.
Chia‐Yun Liu Dr. Ming‐Tsang Tsai Dr. Po‐Yu Tsai Yu‐Ting Liu Si Ying Chen Prof. Agnes Hsiu Hwa Chang Prof. King‐Chuen Lin 《Chemphyschem》2011,12(1):206-216
By employing time‐resolved Fourier transform infrared emission spectroscopy, the fragments HCl (v=1–3), HBr (v=1), and CO (v=1‐3) are detected in one‐photon dissociation of 2‐bromopropionyl chloride (CH3CHBrCOCl) at 248 nm. Ar gas is added to induce internal conversion and to enhance the fragment yields. The time‐resolved high‐resolution spectra of HCl and CO were analyzed to determine the rovibrational energy deposition of 10.0±0.2 and 7.4±0.6 kcal mol?1, respectively, while the rotational energy in HBr is evaluated to be 0.9±0.1 kcal mol?1. The branching ratio of HCl(v>0)/HBr(v>0) is estimated to be 1:0.53. The bond selectivity of halide formation in the photolysis follows the same trend as the halogen atom elimination. The probability of HCl contribution from a hot Cl reaction with the precursor is negligible according to the measurements of HCl amount by adding an active reagent, Br2, in the system. The HCl elimination channel under Ar addition is verified to be slower by two orders of magnitude than the Cl elimination channel. With the aid of ab initio calculations, the observed fragments are dissociated from the hot ground state CH3CHBrCOCl. A two‐body dissociation channel is favored leading to either HCl+CH3CBrCO or HBr+CH2CHCOCl, in which the CH3CBrCO moiety may further undergo secondary dissociation to release CO. 相似文献
485.
486.
Burghart J Sorg A Brückner R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(23):6469-6483
Stereoselective syntheses of 1,6‐bis(tributylstannyl)hexa‐1,3,5‐trienes, 1,8‐bis(tributylstannyl)octa‐1,3,5,7‐tetraenes, and 1,10‐bis(tributylstannyl)deca‐1,3,5,7,9‐pentaenes with various methylation patterns were achieved based on stereocomplementary C?C bond‐forming reactions. All‐E isomers resulted from Ramberg–Bäcklund rearrangements of distannylated diallyl‐, allylpentadienyl‐, or bis‐ (pentadienyl)sulfones. Mono‐Z‐configured 1,ω‐bis(tributylstannyl)‐1,3,5‐polyenes emerged from (Sylvestre–)Julia olefinations of Bu3Sn‐substituted enals or dienals with Bu3Sn‐substituted allyl or pentadienyl benzothiazolylsulfones. Related Ramberg–Bäcklund approaches provided all‐E‐1‐bromo‐6‐(tributylstannyl)hexa‐1,3,5‐triene but not all‐E‐1‐(tetramethyldioxaborolanyl)‐6‐(tributylstannyl)hexa‐1,3,5‐triene. 相似文献
487.
Salomé Llabrés Dr. Esther Vicente‐García Dr. Sara Preciado Cristina Guiu Prof. Ramon Pouplana Prof. Rodolfo Lavilla Prof. F. Javier Luque 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(40):13355-13361
The evolution of a ternary molecular system (imine, diene and nitrile) is analyzed to disclose the pathways leading to a divergent synthetic outcome. The Lewis acid catalyzed reaction between cyclohexadiene, 2‐phenyl‐indol‐3‐one and acetonitrile yields the imino‐Diels–Alder adduct as the major product together with minor amounts of the Mannich–Ritter‐amidine product. The experimental and computational data show that the relative orientation of the initial reactants dictates the synthetic outcome. The exo approach between imine and diene leads to the Diels–Alder adduct in a concerted process, whereas the endo mode leads to a polarized intermediate, which is trapped by acetonitrile to yield the multicomponent adduct. 相似文献
488.
Dr. Sílvia Osuna Dr. Alpay Dermenci Prof. Scott J. Miller Prof. K. N. Houk 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(42):14245-14253
The stereoselective Rauhut–Currier (RC) reaction catalyzed by a cysteine derivative has been explored computationally with density functional theory (M06‐2X). Both methanethiol and a chiral cysteine derivative were studied as nucleophiles. The complete reaction pathway involves rate‐determining elimination of the thiol catalyst from the Michael addition product. The stereoselective Rauhut–Currier reaction, catalyzed by a cysteine derivative as a nucleophile, has also been studied in detail. This reaction was experimentally found to be extremely sensitive to the reaction conditions, such as the number of water equivalents and the effect of potassium counterion. The E1cB process for catalyst elimination has been explored computationally for the eight possible stereoisomers. The effect of explicit water solvation and the presence of counterion (either K+ or Na+) has been studied for the lowest energy enantiomer pair (1S, 2R, 3S)/(1R, 2S, 3R). 相似文献
489.
Walter Vogt 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):123-125
Abstract o-Hydroxybenzyl alcohol reacts with trimethyl phosphite under smooth conditions to o-hydroxyphenylmethane phosphonic acid dimethyl ester. This unusual reaction is of widest applicability. Derivatives of o-hydroxybenzyl alcohol independent of type, number or position of substituents in the ring, react with alkyl esters of phosphorous, phosphonous or phosphinous acids in an analogous process, forming the corresponding o-hydroxyphenylmethane phosphonic or phosphinic esters or phosphine oxides. 相似文献
490.
A highly regio- and stereoselective trans-hydrofluorination of N-sulfonyl ynamides has been realized with AgF as the fluorination reagent, affording (Z)-α-fluoroenamides in good to excellent yields. The reaction proceeds under mild reaction conditions and shows good functional group compatibility. 相似文献