Inverse Regioselectivity Research Articles

Intramolecular Hydroamination of Selenoalkynes to 2-Selenylindoles in the Absence of Catalyst.

In this work, a series of 2-chalcogenylindoles was synthesized by an efficient methodology, starting from chalcogenoalkynes, including a previously unreported tellurium indole derivative. For the first time, these 2-substituted chalcogenylindoles were obtained in the absence of metal catalyst or base, under thermal conditions only. In addition, the results described herein represent a methodology with inverse regioselectivity for the chalcogen functionalization of indoles.

Imines in the Titanium Coordination Sphere: Highly Reactive Titanaaziridines and Larger Titanacycles Formed by Subsequent C–C Coupling Reactions

AbstractThe reductive complexation of aldimines is one of the promising synthetic tools to obtain titanaaziridines by reaction of the corresponding titanium halides and magnesium as a reducing agent. The effects of the substitution pattern of the imine ligand and the nature of the titanium fragment on the degree of activation of the η2‐coordinated N–C double bond were investigated. With Cp#TiCl3 (Cp# = cyclopentadienyl or pentamethylcyclopentadienyl) as the precursor for the reductive complexation of the imines N‐(4‐methylbenzylidene)aniline (2e) and 2‐methyl‐1‐pyrroline (7), the formation of diazatitanacyclopentanes by McMurry‐like C–C coupling is found. A six‐membered titanacycle 8 is obtained by a Michael‐like coupling reaction of 7. By these insights, it is possible to derive a general reaction pattern for low‐valent titanium centers with imines. Three‐membered titanaaziridines are formed for sterically demanding imines. If such a formation is not possible, coupling reactions occur. Imines that have the opportunity to release a proton at the β‐position to the nitrogen atom undergo Michael‐like reactions, whereas McMurry‐like coupling reactions are found at less‐shielded titanium centers. Although the titanoceneaziridines show the expected reactivity with aldehydes, ketones, and nitriles, the insertion of alkynes into the titanium–carbon bond proceeds with a remarkably inverse regioselectivity compared with that for the methyleneaniline complex [CpAd2Ti(η2‐RN=CH2)] (6; Ad = adamantanyl, R = p‐ClC6H4).

ChemInform Abstract: Inverse Regioselectivity in the Silylstannylation of Alkynes and Allenes: Copper‐Catalyzed Three‐Component Coupling with a Silylborane and a Tin Alkoxide.

AbstractReversed regioselectivity, compared to conventional silylstannylation reactions under Pd‐catalysis, is achieved using silyl boranes (II) and tin alkoxides (III) and (VII) in a one‐pot reaction to generate either 2‐silyl‐1‐stannyl‐1‐alkenes (IV)/(V) from alkynes (I) and 1‐silyl‐2‐stannyl‐2‐alkenes (VIII)/(IX) from allenes (VI).

ChemInform Abstract: Borylstannylation of Alkynes with Inverse Regioselectivity: Copper‐Catalyzed Three‐Component Coupling Using a Masked Diboron.

AbstractThe three‐component borylstannylation reaction of terminal alkynes proceeds with inverse regioselectivity in the presence of a copper catalyst using a masked diboron compound giving diverse cis‐boryl(stannyl)alkenes.

Borylstannylation of alkynes with inverse regioselectivity: copper-catalyzed three-component coupling using a masked diboron.

A variety of terminal alkynes are facilely convertible into cis-boryl(stannyl)alkenes with inverse regioselectivity to those of the previous borylstannylation by the copper-catalyzed three-component reaction using a masked diboron. The synthetic utility of the resulting boryl(stannyl)alkenes has been demonstrated by chemoselective coupling reactions.

Inverse regioselectivity in the silylstannylation of alkynes and allenes: copper-catalyzed three-component coupling with a silylborane and a tin alkoxide.

Silylstannylation of alkynes and allenes has been found to proceed by three-component coupling using a silylborane and a tin alkoxide in the presence of a Cu(I) catalyst. The regioselectivities are completely inverse to those of the conventional silylstannylation under palladium catalysis.

ChemInform Abstract: A Synthesis of 1-Azaanthraquinones via Diels-Alder Reaction of 4-Hydroxy- and 4-Methoxy-2-phenylquinolinequinones with 3-Trimethylsilyloxy-1,3-butadienes: Observation of Inverse Regioselectivity.

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Gold Catalysis: Dihydroisobenzofurans and Isochromanes by the Intramolecular Furan/Alkyne Reaction

AbstractA series of furyl alcohols and homofuryl alcohols was synthesized by reduction of furfurals or reaction of furyllithium compounds with epoxides and subsequent propargylation. The gold‐catalyzed cycloisomerization of these products furnished dihydroisobenzofurans and isochromanes. Crystal structure analyses proved the sequence of the substituents for both classes of products. Unsaturated dicarbonyl compounds as side‐products show the mechanistic relationship to the analogous platinum‐catalyzed reactions. Neither ester groups, even on the 4‐position of the furan ring, nor aryl bromides hinder the catalysis by gold. In the case of a substrate with an allyl ether in the side chain, a side‐product, which provides evidence for a reaction of the alkyne with an inverse regioselectivity, was observed.

Reaction of cyclohexanone benzylimines with ethylidenemalonate diesters. Diphenyl 2-ethylidenemalonate: a highly electrophilic synthetic equivalent of crotonic esters.

The diastereoselective Michael alkylation of alpha-substituted and alpha,alpha'-disubstituted cyclohexanone benzylimines with ethylidenemalonate diesters was carried out for mechanistic and synthetic purposes. In the first case, an inverse regioselectivity occurred in comparison with what is generally observed since the Michael adducts resulted from alkylation of the non substituted enamine tautomer. With alpha,alpha'-disubstituted imines, in all cases, the stereochemistry of the major diastereomer was the one anticipated from a mechanism including a chairlike complex approach with a preferred exo position for the beta-methyl group of the ethylidenemalonic acid diesters. Furthermore, diphenyl 2-ethylidenemalonate 4 was found to be a highly electrophilic synthetic equivalent of crotonic esters.

Umpolung of P−H Bonds

The π-electron delocalization in the diazaphospholenes 1 leads not only to a weakening of the P−H bond, but also to an umpolung of its reactivity. Thus, compounds 1 react with acids with elimination of H2, and display an inverse regioselectivity during the addition to benzaldehyde. R1=H, Cl; R2=tBu, 2,4,6-Me3C6H2.

A Synthesis of 1-Azaanthraquinones via Diels-Alder Reaction of 4-Hydroxy- and 4-Methoxy-2-phenylquinolinequinones with 3-Trimethylsilyloxy-1,3-butadienes: Observation of Inverse Regioselectivity.

Diels-Alder reaction of 4-hydroxy-2-phenylquinolinequinone (10a) and 4-methoxy-2-phenylquinoline-quinone (10b) with 1-methoxy-3-trimethylsilyloxybutadiene proceeded in a highly regio- and stereoselective manner to give the [4+2] adducts (11) and (14) in good yields, respectively. The structures of the adducts and their derivatives were unambiguously determined by spectroscopic data, including high resolution heteronuclear multi bond correlation. The quinolinequinones (10a and 10b) gave inverse regioselectivity. This is related to the presence of the hydroxy group or the methoxy group at the C-4 position. These results demonstrated that Diels-Alder reaction of azadienophiles with activated dienes provides a versatile method for synthesizing 4-oxygenated 1-azaanthraquinones.

Intramolecular Cycloaddition of the Azomethine Ylides Derived from α-Amino Acids or Esters and 5-Oxo-6-heptenals or 4-Oxo-5-hexenals

Abstract Intramolecular cycloadditions of the azomethine ylides bearing a carbonyl-activated olefinic moiety, generated from α-amino acids or esters and 5-oxo-6-heptenals or 4-oxo-5-hexenals, produce the stereoselective internal cycloadducts either to olefin or carbonyl dipolarophilic function with normal or inverse regioselectivity, depending upon the types of ylides as well as the intervening chain length. Exclusively high diastereofacial selectivity has been achieved when 2-phenyl-4-thiazolidinecarboxylic acid and its methyl ester are utilized.