Synthesis regioselectivity

A regioselective synthesis of 2-amino[l, 2,4]triazinones 708 was reported (82JHC1583 83JHC1671) by reaction of 706 with 0-(2,4-dinitrophenyl)-hydroxylamine 707 as an amino transfer agent. Subsequent reaction of 708 with ammonia or amines, followed by ring closure with formic acid, provided 709. 

A11 elegant application of the strategy based on the appropriate use of a 6-exo or 6-endo cyclization of a 5- or y-epoxy alcohol, respectively, to give corresponding adjacent or fused THP rings can be found in the regioselective synthesis of the ABC tris-THP core of thyrsiferol and venustatriol [29b]. 

Allylation of acyloyl-imidazoles and pyrazoles61 with allyl halide mediated by indium in aqueous media provides a facile regioselective synthesis of P, y-unsaturated ketones (Scheme 11.1), which has been applied to the synthesis of the monoterpene artemesia ketone. The same product can be obtained by indium-mediated allylation of acyl cyanide (Eq. 11.35).62 Samarium, gallium, and bismuth can be used as a mediator for the allylation of nitrones and hydrazones to give homoallylic hydroxylamine and hydrazides in aqueous media in the presence of Bu4NBr (Scheme 11.2).63 The reaction with gallium and bismuth can be increased dramatically under microwave activation. 

A thio-Claisen rearrangement174 was used for the regioselective synthesis of thiopyrano[2,3-b]pyran-2-ones and thieno[2,3-b]pyran-2-ones (Eq. 12.76). A convenient method for the aromatic amino-Claisen rearrangement of N-(l,l-disubstituted-allyl)anilines led to the 2-allylanilines being produced cleanly and in high yield by using a catalytic amount of p-toluenesulfonic acid in acetonitrile/water (Eq. 12.77).175... 

Selective transformations Selective styrene ring opening [103] One-pot domino process for regioselective synthesis of a-carbonyl furans [104] Tandem process for synthesis of quinoxalines [105] Atmospheric oxidation of toluene [106] Cyclohexane oxidation [107] Synthesis of imines from alcohols [108] Synthesis of 2-aminodiphenylamine [109] 9H-Fluorene oxidation [110] Dehydrogenation of ethane in the presence of C02 [111] Decomposition of methane [112] Carbon monoxide oxidation [113]... 

A versatile and regioselective synthesis of benzo[b]furans, naphthalenes, indoles and benzothiophenes was achieved by reaction of o-alkynylarene and heteroarene carboxaldehyde derivatives in the presence of iodonium ions. The reaction mechanism was also discussed <06CEJ5790>. 

Hydrazones are also useful substrates in the preparation of pyrazoles. Reaction of N-monosubstituted hydrazones with nitroolefins led to a regioselective synthesis of substituted pyrazoles <060L3505>. lf/-3-Ferrocenyl-l-phenylpyrazole-4-carboxaldehyde was achieved by condensation of acetylferrocene with phenylhydrazine followed by intramolecular cyclization of the hydrazone obtained under Vilsmeier-Haack conditions <06SL2581>. A one-pot synthesis of oxime derivatives of l-phenyl-3-arylpyrazole-4-carboxaldehydes has been accomplished by the Vilsmeier-Haack reaction of acetophenone phenylhydrazones <06SC3479>. 

Reductive cleavage of 5-silyl-, 3-, 4-, and 5-silylmethylisoxazoles 1 gave silyl (3-enaminones 2, useful synthons in the regioselective synthesis of silyl- and silylmethylpyrazoles 3, as well as pyrrole-, pyrimidine-, and pyridine derivatives <06T611>. 

Direct C-Harylation of purines in position 8 by diverse aryl iodides has been achieved with Pd catalysis in the presence of Cul and CS2CO3. The methodology is general and efficient and was applied in the consecutive regioselective synthesis of 2,6,8-trisubstituted purines bearing three different C-substituents in combination with two cross-coupling reactions... 

Negishi et al. reported the regioselective synthesis of diisoalkyl derivatives from monosubstituted alkenes in yields ranging from 58-95%, Scheme 8, from the in situ prepared ethylene complex Cp2Zr(C2H4).35 The zirconocene-ethylene complex presumably undergoes alkene insertion to furnish a zirconacyclopentane which further reacts with diethylzinc to yield the diisoalkylzinc compound. 

Stereo- and regioselective synthesis of trienes and tetraenes has been reported by palladium-catalysed coupling of (E)- or (Z)-l-alkenyl boronates with (E)- or (Z)-2-bromo-1-phenylthio-l-alkenes followed by treatment with a Grignard reagent in the presence of a nickel catalyst (equation 146)259. 

Witulski introduced a novel protocol for crossed alkyne cyclotrimerizations of systems such as 87 mediated by Grubb s catalyst to produce 4,6-disubstituted indolines 88 <00CC1965>. Interestingly, use of Wilkinson s catalyst [RhCl(PPhj)3] allows for the regioselective synthesis of the corresponding 4,5-substituted isomers. 

Methods for the synthesis of substituted pyridines remains an intense topic of research. One of the most popular approaches to substituted pyridines remains cycloaddition reactions. While this strategy is not new and many examples are in the current literature <00TL10251>, the state-of-the-art has been expanded. Weinreb and co-workers have reported the regioselective synthesis of pyridines (3) via intramolecular oximino malonate hetero Diels-Alder reactions (1 - 2) <00OL4007>. Similarly, the intramolecular [4 + 2] cycloaddition of... 

Very recently, Kong has incorporated refinements to this approach and illustrated its potential with the regioselective synthesis of a large variety of oligosaccharides... 

Abstract The development of a new method for the regioselective synthesis of functionalized indoles and six-membered benzo-fused N-, O-, and S-heterocycles is reported. The key step involves the generation of a benzyne-tethered vinyl or... 

Shimizu and Tsuji [4] reported the first highly regioselective synthesis of 1,2-di-substituted allylic amines through capture of a Jt-allylpalladium complex by pyrrolidine (Scheme 16.2). This methodology has since been extended to a wide range of amines and allenes [5]. 

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