- Hydroheteroarylation of Unactivated Alkenes Using N-Methoxyheteroarenium Salts
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We report the first reductive coupling of unactivated alkenes with N-methoxy pyridazinium, imidazolium, quinolinium, and isoquinolinium salts under hydrogen atom transfer (HAT) conditions, and an expanded scope for the coupling of alkenes with N-methoxy pyridinium salts. N-Methoxy pyridazinium, imidazolium, quinolinium, and isoquinolinium salts are accessible in 1-2 steps from the commercial arenes or arene N-oxides (25-99%). N-Methoxy imidazolium salts are accessible in three steps from commercial amines (50-85%). In total 36 discrete methoxyheteroarenium salts bearing electron-donating, electron-withdrawing, alkyl, aryl, halogen, and haloalkyl substituents were prepared (several in multigram quantities) and coupled with 38 different alkenes. The transformations proceed under neutral conditions at ambient temperature, provide monoalkylation products exclusively, and form a single alkene addition regioisomer. Preparatively useful and complementary site selectivities in the addition of secondary and tertiary radicals to pyidinium salts are documented: harder secondary radicals favor C-2 addition (2->10:1), while softer tertiary radicals favor bond formation to C-4 (4.7->29:1). A diene possessing a 1,2-disubstituted and 2,2-disubstituted alkene undergoes hydropyridylation at the latter exclusively (61%) suggesting useful site selectivities can be obtained in polyene substrates. The methoxypyridinium salts can also be employed in dehydrogenative arylation, borono-Minisci, and tandem arylation processes. Mechanistic studies support the involvement of a radical process.
- Ma, Xiaoshen,Dang, Hester,Rose, John A.,Rablen, Paul,Herzon, Seth B.
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supporting information
p. 5998 - 6007
(2017/05/04)
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- One-pot method for regioselective bromination and sequential carbon-carbon bond-forming reactions of allylic alcohol derivatives
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An efficient one-pot method for the regioselective bromination of allylic alcohol derivatives (two-step reaction sequence) followed by Sonogashira, Negishi, or Suzuki-Miyaura coupling reactions in the same reaction vessel (three-step reaction sequence) ha
- Kutsumura, Noriki,Matsubara, Yusuke,Niwa, Kentaro,Ito, Ai,Saito, Takao
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p. 3337 - 3346
(2013/06/27)
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- 2-(Selenocyanatomethyl)-2-propenol-A convenient synthon for ligation via the deselenative allylic rearrangement of allyl selenosulfides: Preparation, functional group compatibility, and application
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The preparation and reactions of 2-(selenocyanatomethyl)-2-propenol are described and reveal the compatibility of the allylic selenocyanate group with a range of mild oxidizing and Lewis acidic conditions. 2-(Selenocyanatomethyl)-2- propenol and its derivatives are employed in the functionalization of simple and amino acid derived thiols in methanolic solution at room temperature to give 2-(hydroxymethyl)allyl sulfides in good to excellent yield.
- Lachkar, David,Boudet, Caroline,Guinchard, Xavier,Crich, David
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p. 944 - 953
(2013/02/22)
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- A mild method for the protection of alcohols using a para-methoxybenzylthio tetrazole (PMB-ST) under dual acid-base activation
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With a view to expand the repertoire of chemoselective methods applicable to sensitive and multifunctional substrates, the p-methoxybenzylation of alcohols under essentially neutral conditions is reported. This was achieved by the silver triflate (AgOTf) activation of 5-(p-methoxybenzylthio)-1-phenyl-1H-tetrazole (PMB-ST) in the presence of 2,6-di-tert-butyl-4-methylpyridine (DTBMP).
- Kotturi, Santosh R.,Tan, Jason S.,Lear, Martin J.
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supporting information; experimental part
p. 5267 - 5269
(2009/12/24)
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- The total synthesis and biological evaluation of nafuredin-γ and its analogues
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Nafuredin (1) is converted to nafuredin-γ (2) under mild basic conditions and both compounds exhibit the same inhibitory activity and selectivity against NADH-fumarate reductase (complex I). The total synthesis of 2 was achieved by a convergent approach u
- Nagamitsu, Tohru,Takano, Daisuke,Seki, Miyuki,Arima, Shiho,Ohtawa, Masaki,Shiomi, Kazuro,Harigaya, Yoshihiro,Omura, Satoshi
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p. 8117 - 8127
(2008/12/21)
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- Enantioselective total synthesis and determination of the absolute configuration of the 4,6,8,10,16,18-hexamethyldocosane from Antitrogus parvulus
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The absolute and relative configuration of the hexamethyldocosane (1) isolated from the cuticula of Antitrogus parvulus was determined based on the total synthesis of both diastereomers 1a and 1b in enantiomerically pure form. The synthesis demonstrates t
- Herber, Christian,Breit, Bernhard
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p. 3512 - 3519
(2008/02/12)
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- Synthesis of the C29-C44 portion of spongistatin 1 (altohyrtin A)
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Two synthetic approaches to the C29-C44 portion of spongistatin 1 (ahohyritin A) have been developed. The key step of the first approach relies on the Claisen rearrangement of glucal 18 to provide ester 20a. This intermediate was advanced to silyl enol ether 30, which was coupled under Mukaiyama aldol conditions with aldehyde 3. Cyclization of this aldol adduct completed our first synthesis of the C29-C44 portion of spongistatin 1, requiring 25 total steps and occurring in 2.4% yield over the longest linear sequence (21 steps). We have also developed a second-generation approach based on the C-glycosidation of glucal 43. Through equilibration of the corresponding C-glycosides 49a/b and 50a/b the desired C-glycoside (50a) was obtained in good yield. Aldol condensation of this ketone provided cyclization precursor 67, which undergoes acid-catalyzed ketalization to close the E-ring of the spongistatins. An oxidation/reduction protocol was employed to set the C37 stereocenter. Protection of the C37 carbonol and selective unmasking of the C44 carbonol completed our second generation synthesis. This approach requires 27 steps and occurred in 13-2% yield over the longest linear sequence (18 steps).
- Wallace, Grier A.,Scott, Robert W.,Heathcock, Clayton H.
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p. 4145 - 4152
(2007/10/03)
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- Mechanistic aspects of the zeolite β induced rearrangement of alkoxybenzyl allyl ethers to aldehydes and ketones
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The mechanism for the novel zeolite β catalyzed rearrangement of alkoxybenzyl allyl ethers to aldehydes and ketones has been investigated by use of cross reactions and deuterium labeling. The reaction is mainly intramolecular and may be described as a nucleophilic attack of the double bond on the electrophilic benzylic carbon of the ether-Lewis acid complex, followed by a 1,2-hydride (or alkyl) migration. Acta Chemica Scandinavica 1998.
- Wennerberg, Johan,Frejd, Torbjoern
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- Zeolite β-Induced Rearrangement of Alkoxybenzyl Allyl Ethers to Aldehydes and Ketones. 5.1 Variation of the Allylic Moiety
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Allylic PMB ethers rearranged in the presence of zeolite β to form 4-arylbutanals or 5-arylpentanones depending on the substituent pattern of the allylic moiety. Best results were obtained with substrates carrying simple substituents in the allylic 2-posi
- Wennerberg, Johan,Olofsson, Charlotte,Frejd, Torbjoern
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p. 3595 - 3598
(2007/10/03)
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