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31.
Srikrishna Bera Dr. Constantin G. Daniliuc Prof. Dr. Armido Studer 《Angewandte Chemie (International ed. in English)》2017,56(26):7402-7406
An efficient method for the asymmetric intramolecular dearomatization of indoles by using oxidative N-heterocyclic carbene catalysis is demonstrated. Valuable optically active spirocyclic indolenines bearing an all-carbon quaternary stereocenter are obtained in excellent yields and with excellent enantioselectivity. The starting indoles are readily prepared and the reactions proceed through an intramolecular indole 3-acylation with an in situ generated acyl azolium intermediate to form a spirocyclic ketone moiety. 相似文献
32.
Srikrishna Bera Xile Hu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(39):13992-13997
Metal hydride catalyzed hydrocarbonation reactions of alkenes are an efficient approach to construct new carbon–carbon bonds from readily available alkenes. However, the regioselectivity of hydrocarbonation remains challenging to be controlled. In nickel hydride (NiH) catalyzed hydrocarbonation, linear selectivity is most often obtained because of the relative stability of the linear Ni–alkyl intermediate over its branched counterpart. Herein, we show that the boronic pinacol ester (Bpin) group directs a Ni‐catalyzed hydrocarbonation to occur at its adjacent carbon center, resulting in formal branch selectivity. Both alkyl and aryl halides can be used as electrophiles in this hydrocarbonation, providing access to a wide range of secondary alkyl Bpin derivatives, which are valuable building blocks in synthetic chemistry. The utility of the method is demonstrated by the late‐stage functionalization of natural products and drug molecules, the synthesis of an anticancer agent, and iterative syntheses. 相似文献
33.
[structure: see text] By total synthesis, mycolactone C has been established as an approximately 1:1 mixture of Z-Delta4'5'- and E-Delta4'5'-geometric isomers of C12'-deoxymycolactones A and B. 相似文献
34.
Adusumilli Srikrishna Vijendra H. Pardeshi Gedu Satyanarayana 《Tetrahedron: Asymmetry》2010,21(6):746-750
Enantioselective formal total syntheses of the marine trisnorsesquiterpenes clavukerin A and isoclavukerin A, starting from (R)-limonene employing an RCM reaction as the key step, are described. 相似文献
35.
Enantiospecific syntheses of diquinane and linear triquinanes were accomplished, starting from the readily available α-campholenaldehyde employing a Nazarov reaction as the key step. 相似文献
36.
This paper investigates a queueing system in which the controller can perform admission and service rate control. In particular, we examine a single-server queueing system with Poisson arrivals and exponentially distributed services with adjustable rates. At each decision epoch the controller may adjust the service rate. Also, the controller can reject incoming customers as they arrive. The objective is to minimize long-run average costs which include: a holding cost, which is a non-decreasing function of the number of jobs in the system; a service rate cost c(x), representing the cost per unit time for servicing jobs at rate x; and a rejection cost κ for rejecting a single job. From basic principles, we derive a simple, efficient algorithm for computing the optimal policy. Our algorithm also provides an easily computable bound on the optimality gap at every step. Finally, we demonstrate that, in the class of stationary policies, deterministic stationary policies are optimal for this problem. 相似文献
37.
Dr. David L. Cramer Srikrishna Bera Prof. Dr. Armido Studer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(22):7403-7407
The utility of oxidative NHC catalysis for both the regioselective and chemoselective functionalization of carbohydrates is explored. Chiral NHCs allow for the highly regioselective oxidative esterification of various carbohydrates using aldehydes as acylation precursors. The transformation was also shown to be amenable to both cis/trans diol isomers, free amino groups, and selective for specific sugar epimers in competition experiments. Efficiency and regioselectivity of the acylation can be improved upon using two different NHC catalysts that act cooperatively. The potential of the method is documented by the regioselective acylation of an amino‐linked neodisaccharide. 相似文献
38.
An enantiospecific approach to mayurone and thujopsenes, sesquiterpenes containing three contiguous quaternary carbon atoms, starting from (R)-carvone (8), is described. (S)-3,4,4-Trimethylcarvone (7), obtained from (R)-carvone, was transformed into the bicyclo[2.2.2]octanone 13 via regioselective intramolecular alkylation of the allyl bromide 11. Regioselective ozonolysis and Criegee fragmentation of the bicyclic ketone 13 furnished the keto ester 14. Reductive deoxygenation followed by one-carbon homologation transformed the keto ester 19 into the ester 6. Intramolecular cyclopropanation of the diazo ketone 25, derived from the acid 5, furnished (-)-dihydromayurone (4), thus constituting a formal enantiospecific synthesis of mayurone and thujopsenes. 相似文献
39.
Goverdhan Mehta Vishwakarma Singh A. Srikrishna T. Stanley Cameron Christine Chan 《Tetrahedron letters》1979,20(47):4595-4598
A serendipitious cationic rearrangement of hexacyclic propellane to its strained fluxional isomer, the bridged 1,3,5-cyclooctatriene is described. 相似文献
40.
An enantiospecific total synthesis of patchouli alcohol, starting from the readily available monoterpene (R)-carvone, has been accomplished. A tandem double Michael reaction–alkylation sequence and single electron mediated 6-endo trig cyclisation reaction have been employed as key steps. 相似文献