- Bromomethyl Silicate: A Robust Methylene Transfer Reagent for Radical-Polar Crossover Cyclopropanation of Alkenes
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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
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supporting information
p. 1778 - 1781
(2020/03/11)
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- ASYMMETRIC CYCLOPROPANATION
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The present invention provides a method for asymmetric cyclopropanation of olefins comprising admixing an olefin, an enantiomerically enriched amino acid derivative, and a (halomethylene)zinc compound under conditions sufficient to produce an enantiomeric
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Page/Page column 13-15; 17-18
(2010/02/11)
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- A Novel Class of Tunable Zinc Reagents (RXZnCH2Y) for Efficient Cyclopropanation of Olefins
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A class of zinc reagents (RXZnCH2Y) generated with an appropriate organozinc is very effective for the cyclopropanation of olefins. The reactivity and selectivity of these reagents can be regulated by tuning the electronic and steric nature of the RX group on Zn. A reasonable level of enantioselectivity was obtained for the cyclopropanation of unfunctionalized olefins when a chiral (iodomethyl)zinc species was used, providing a valuable approach for the asymmetric cyclopropanation of unfunctionalized olefins.
- Lorenz, Jon C.,Long, Jiang,Yang, Zhiqiang,Xue, Song,Xie, Yinong,Shi, Yian
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p. 327 - 334
(2007/10/03)
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- Thermochemistry of Phenyl-Substituted Benzobicyclohex-2-enes
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The thermal rearrangements of benzobicyclohex-2-ene (21) and its phenyl-substituted analogues 22-25 (Scheme V) as models of sterically constrained phenylcyclopropanes have been studied by means of flash vacuum pyrolysis.In most cases the major pathway was cleavage of the "internal" C(1)-C(5) cyclopropane bond followed by a 1,2-hydrogen or a 1,2-phenylshift in the resulting biradical.For 6-phenylbenzobicyclohex-2-ene (25), substantial cleavage of the "external" C(1)-C(6) cyclopropane bond was observed, the phenyl substitution pattern being favorable for stabilization of the resulting biradical 62.Phenyl-substituted 1,2-dihydronaphthalenes 44, 47, 51, and 55 are among the major products.Comparison of the plots of the pyrolysis product composition of the 1,2-dihydronaphthalenes vs. pyrolysis temperature with similar plots of the title compounds (22-25) suggested that some of the minor products, viz., the 1,2-divinylbenzenes 31, 42, and 49, are formed via carbenes 30, 41, 50, 57, and 61 rather than via biradicals.Especially at higher pyrolysis temperatures, a large amount of an oxidation product, viz., 1- or 2-phenylnaphthalene (48 or 54), is formed.
- Lamberts, Joseph J.,Laarhoven, Wim H.
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p. 100 - 106
(2007/10/02)
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- Photochemistry of Phenyl-Substituted Benzobicyclohex-2-enes. A Reverse Di-?-methane Rearrangement
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The photochemical rearrangements of phenyl-substituted benzobicyclohex-2-enes can generally be explained by assuming that homolytic fission of that cyclopropane bond which leads to the most stable diradical is the primary step.The final products are formed by 1,2 hydrogen shifts in the intermediate.An exception to this general pattern was observed with 5-phenylbenzobicyclohex-2-ene (5).The photoproducts of 5 could only be explained by assuming reverse di-?-methane rearrangements followed by 1,3 hydrogen shifts.It is argued that this reaction path is followed because of the high rate to the back-reaction of the homolytic bond fission of 5.
- Lamberts, Joseph J. M.,Laarhoven, Wim H.
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p. 2202 - 2206
(2007/10/02)
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- SYNTHESIS AND ELECTROPHILIC REACTIONS OF A CONFORMATIONALLY RIGID CYCLOPROPYLCARBINYL CATION. AN UNUSUAL SYNTHESIS OF SUBSTITUTED BENZAZULENES.
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A tropylium-substituted cyclopropane has been prepared which is rigidly held in the "bisected" conformation.Its electrophilic reactions are also investigated.
- Jason, Mark E.
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p. 1635 - 1638
(2007/10/02)
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