- Bromomethyl Silicate: A Robust Methylene Transfer Reagent for Radical-Polar Crossover Cyclopropanation of Alkenes
-
A general protocol for visible-light-induced cyclopropanation of alkenes was developed with bromomethyl silicate as a methylene transfer reagent, offering a robust tool for accessing highly valuable cyclopropanes. In addition to α-aryl or methyl-substituted Michael acceptors and styrene derivatives, the unactivated 1,1-dialkyl ethylenes were also shown to be viable substrates. Apart from realizing the cyclopropanation of terminal alkenes, the methyl transfer reaction has been further demonstrated to be amenable to the internal olefins. The photocatalytic cyclopropanation of 1,3-bis(1-arylethenyl)benzenes was also achieved, giving polycyclopropane derivatives in excellent yields. With late-stage cyclopropanation as the key strategy, the synthetic utility of this transformation was also demonstrated by the total synthesis of LG100268.
- Luo, Wenping,Fang, Yewen,Zhang, Li,Xu, Tianhang,Liu, Yongjun,Li, Yan,Jin, Xiaoping,Bao, Jiakan,Wu, Xiaodong,Zhang, Zongyong
-
p. 1778 - 1781
(2020/03/11)
-
- Intermolecular scandium triflate-promoted nitrene-transfer [5 + 1] cycloadditions of vinylcyclopropanes
-
Sc(OTf)3-promoted [5 + 1] cycloaddition of vinylcyclopropanes with PhINTs is reported, enabling the regioselective preparation of a range of 1,2,3,6-tetrahydropyridine scaffolds under mild conditions. This represents the second example of a [5
- Laudenschlager, Julie E.,Combee, Logan A.,Hilinski, Michael K.
-
p. 9413 - 9417
(2019/11/14)
-
- Oxidative Ring Contraction of Cyclobutenes: General Approach to Cyclopropylketones including Mechanistic Insights
-
An original oxidative ring contraction of easily accessible cyclobutene derivatives for the selective formation of cyclopropylketones (CPKs) under atmospheric conditions is reported. Comprehensive mechanistic studies are proposed to support this novel, yet unusual, rearrangement. Insights into the mechanism ultimately led to simplification and generalization of the ring contraction of cyclobutenes using mCPBA as an oxidant. This unique and functional group tolerant transformation proceeds under mild conditions at room temperature, providing access to a new library of polyfunctionalized motifs. With CPKs being attractive and privileged pharmacophores, the elaboration of such a simple and straightforward strategy represents a highly valuable tool for drug discovery and medicinal chemistry. Additionally, the described method was employed to generate a pool of bioactive substances and key precursors in a minimum number of steps.
- Baumann, Andreas N.,Schüppel, Franziska,Eisold, Michael,Kreppel, Andrea,De Vivie-Riedle, Regina,Didier, Dorian
-
p. 4905 - 4921
(2018/05/17)
-
- Another Role of Copper in the SimmonsSmith Reaction: Copper-catalyzed Nucleophilic Michael-type Cyclopropanation of a,β-Unsaturated Ketones
-
Cyclopropanation was performed using the Furukawa procedure with CH2I2/Et2Zn and a,β-unsaturated ketones. The reaction was performed in the presence of a copper salt. The reactivity was highly dependent on the substrate structure, and cyclopropanated products were obtained in better yields than those achieved using the original SimmonsSmith conditions with a ZnCu couple in some cases. Stereospecificity was observed in a certain case; however, the synthesis of an asymmetric version with a chiral ligand was not successful.
- Fujii, Kanami,Misaki, Tomonori,Sugimura, Takashi
-
p. 634 - 636
(2014/05/20)
-
- Polymer-mediated pinacol rearrangements
-
Both poly(3,4-ethylenedioxythiophene) and poly(pyrrole) mediate a pinacol rearrangement of 1,2-diols. The yields of ketone or aldehyde products are comparable to those observed for treatment with mineral acids or Lewis acids. The advantage of this protocol is a two-phase reaction medium in hydrocarbon solvents that allows facile recovery of the products by simple filtration of the polymer and removal of solvents. Both the polymer and the hydrocarbon solvent may be recovered and used in subsequent reactions. Georg Thieme Verlag Stuttgart · New York.
- Pavlik, Christopher,Morton, Martha D.,Smith, Michael B.
-
p. 2191 - 2194
(2011/11/06)
-
- Addition of dichloro- and dibromocarbene to 1,2-diphenylcyclobutene
-
1,2-Diphenylcyclobutene (7) was reacted with dibromo- and dichlorocarbene, both generated via three different methods. 1,3-Diphenyl-2-halocyclopenta-1,3-dienes 12 were isolated which result from addition of the dihalocarbenes to the cyclobutene double bond of 7. A cationic cyclopropyl-allyl rearrangement (CCA) in gem-dihalobicyclopentanes 8 leads to 2,3-dihalocyclopentenes 9, which under the reaction conditions are dehydrohalogenated to 12. A second carbene addition and rearrangement afford aromatic compounds 11 and 16.
- Wagner, Robert A.,Weber, Juergen,Brinker, Udo H.
-
p. 246 - 247
(2007/10/03)
-
- SURFACE PHOTOCHEMISTRY: A "SYMMETRY FORBIDDEN" SIGMATROPIC HYDROGEN SHIFT MEDIATED BY CdS.
-
Excitation of CdS in the absence of oxygen in the presence of cyclic derivatives of diphenylcyclobutene gave the cation radical of the latter which underwent a reversible double bond migration.The structures of the products were established on the basis of spectral data ((1)H, (13)C NMR, MS, UV).Tests were performed to show that the reaction proceeds, at least in part, intramolecularly, and, therefore, represents the first example of a suprafacial sigmatropic hydrogen shift via a radical cation.This suprafacial pathway is symmetry forbidden in closed shell systems.Oxidation products were isolated when the irradiation was performed in an aerated system.The use of excited 9,10-dicyanoanthracene as an electron acceptor did not lead to the expected products; instead the sensitizer was consumed and two thermally unstable products were isolated.Their formation could be quenched by 1,2,4-trimethoxybenzene.
- Mayo, Paul de,Wenska, Grazyna
-
p. 1661 - 1670
(2007/10/02)
-
- Reactions of Spiro
-
Methylenefluorene 3a adds regiospecifically to aryl azides 4 to give the corresponding spiro 5, which lead to the ring-enlargement products, 9-(arylamino)phenanthrenes (9), by pyrolysis and acid-induced reaction.Benzylidenefluorene 3b
- Hirakawa, Kiyoichi,Tanabiki, Yukio
-
p. 280 - 284
(2007/10/02)
-