- Formal total syntheses of alkannin and shikonin
-
A short synthesis of a key intermediate in Nicolaou's syntheses of alkannin and shikonin is described.
- Kim, Ju-Cheun,Jung, Jae-Chul,Park, Oee-Sook
-
-
Read Online
- First Stereoselective Total Synthesis of a Dimeric Naphthoquinonopyrano-γ-lactone: (+)-γ-Actinorhodin
-
We have accomplished the first total synthesis of an isomerically pure naphthoquinonopyrano-γ-lactone dimer, γ-actinorhodin, in eleven steps. Two steps exploit pairs of peri-MeO groups as unusual selectivity controls. The respective MeO groups convey the steric bulk of a bromo or iodo substituent located ortho to one MeO group as steric hindrance into the vicinity of the second MeO group. This relay effect was indispensable for exerting regiocontrol in an aromatic bromination and diastereocontrol in an oxa-Pictet–Spengler cyclization. The absolute configuration of our target compound was established in an asymmetric Sharpless dihydroxylation of a β,γ-unsaturated ester, which was synthesized in a Heck coupling of a bromoiodonaphthalene with ethyl vinylacetate. The dihydroxylation provided the γ-hydroxylactone moiety of the bromonaphthalene that was used as the substrate in the oxa-Pictet–Spengler cyclization. Dimerization to the core of γ-actinorhodin occurred by two Suzuki couplings.
- Neumeyer, Markus,Brückner, Reinhard
-
supporting information
p. 3383 - 3388
(2017/03/17)
-
- Enantioselective Total Syntheses of (R)- A nd (S)-Naphthotectone, and Stereochemical Assignment of the Natural Product
-
Both isomers of naphthotectone, an isoprenoid quinone from Verbenaceae Tectona grandis possessing interesting biological activities, were enantioselectively obtained by two different synthetic routes in which the carbon side-chain of the naphthoquinone core was introduced using either a Sonogashira or a Heck coupling reaction. In both cases, the naphthoquinone core of the final products was obtained by a late-stage anodic treatment. (R)-Naphthotectone was obtained in six steps from leuconaphthazarin with an overall yield of 38 % and an enantiomeric excess of 86 %. This compound was found to have the same absolute configuration as the natural product at its C-3′ stereogenic center. (S)-Naphthotectone was obtained in five steps from leuconaphthazarin with an overall yield of 36 % and an enantiomeric excess of 80 %. Naphthotectone was synthesized in both racemic and enantioenriched forms by two different synthetic strategies using Pd coupling reactions and anodic treatment as key steps. The stereochemistry of the natural product has been assigned.
- Guerrero-Vásquez, Guillermo A.,Galarza, Flávia A. D.,Molinillo, José M. G.,Andrade, Carlos Kleber Z.,Macías, Francisco A.
-
supporting information
p. 1599 - 1604
(2016/04/05)
-
- A convenient synthesis of 2-formyl-1,8:4,5-bis(methylenedioxy) naphthalene
-
2,3-Dihydronaphazarin was prepared from 1,4-dimethoxybenzene and dichloromaleic anhydride. Reaction with bromochloromethane gave 1,8:4,5-bis(methylenedioxy)naphthalene which with NBS, gave 2-bromo-1,8:4,5-bis- (methylenedioxy)naphthalene. Reaction of the Grignard derivative with DMF afforded 2-formyl-1,8:4,5-bis(methylenedioxy)naphthalene. This method had several advantages compared with the reported synthesis, including fewer steps, milder condition and higher yields.
- Zhao, Ai-Hong,Xu, De-Feng,Zhuo, Wen,Rao, Zhen,Li, Shao-Shun
-
p. 647 - 648
(2008/09/17)
-
- Concise and efficient total syntheses of alkannin and shikonin
-
Two enantiomic natural products with wound-healing properties, alkannin (1) and shikonin (2), are accessible by a short and efficient total synthesis. The success was achieved by a novel protecting system for masking of 5,8-dihydroxy-1,4-naphthoquinones (naphthazarins) and a highly stereoselective ketone reduction.
- Nicolaou,Hepworth, David
-
p. 839 - 841
(2007/10/03)
-
- Naphtho-1,3-dioxines
-
Treatment of 1,8-Dihydroxy-naphthaline with bromochloromethane/K2CO3 in DMF gives Naphtho-1,3-dioxine (1a) in good yield.The bromo (1b) and nitro compound (1c) can be obtained free of isomerics by electrophilic substitution of 1a.Bromolithium exchange of 1b leads to a lithium organic compound, which possibles the synthesis of alkyl-, olefinic-, and carboxylic derivatives of the substrate 1a.In a similar way the treatment of 2,3-dihydroxynaphthazarin with chlorobromomethane/K2CO3 gives the naphtho-bis-1,3-dioxine (3a).The substrate 3a can besubjected to electrophilic aromatic substitutions. - Key words: 6-Brom-naphtho-1,3-dioxine, 6-Nitro-naphtho-1,3-dioxine, 4-Methyl-naphthobis-1,3-dioxine-9-carboxylic Acid
- Dallacker, Franz,Jacobs, Johannes,Coerver, Wim
-
p. 1000 - 1007
(2007/10/02)
-