A short route to 3-alkynyl-4-bromo(chloro)cinnolines by Richter-type cyclization of ortho-(dodeca-1,3-diynyl)aryltriaz-1-enes

Cleavage of ortho-(dodeca-1,3-diynyl)triazenes in HCl or HBr medium and subsequent cyclization of the resulting diazonium salts is investigated. In the absence of a strong electron-withdrawing substituent, the reaction affords 3-alkynyl-4-bromo(chloro)cinnolines as the only product. A methoxycarbonyl group promotes hydrolysis of 4-halocinnolines which results in the formation of by-products: furo[3,2-c]cinnoline and cinnolinone. Substitution of bromine in 3-(alk-1-ynyl)-4-bromocinnolines is achieved with methylamine, Na₂S and ethynylbenzene affording pyrrolo[3,2-c]cinnoline, thieno[3,2-c]cinnoline and 3,4-diethynylcinnoline, respectively.     

Palladium-catalyzed coupling of vinyl tosylates with arylsulfinate salts

The first palladium-catalyzed coupling of vinyl tosylates with arylsulfinate salts is described. A variety of cyclic and acyclic vinyl tosylates were coupled with aryl sulfinate salts using 2.5 mol % Pd₂(dba)₃/5.0 mol % XantPhos to give vinyl aryl sulfone products in good yields. The coupling was extended to the preparation of a cyclopropyl vinyl sulfone.     

Heteroaromatic Tosylates as Electrophiles in Regioselective Mizoroki–Heck‐Coupling Reactions with Electron‐Rich Olefins

Easy and direct : Regioselective Mizoroki–Heck‐coupling reactions using heteroaromatic tosylates as electrophiles were achieved, thus providing direct and easy access to highly functionalized α‐heteroarylvinyl amides and ethers.

     

Solvent Effect on Solvolytic Reactivities of 1-Aryl-2,2-Dimethyl-1-Propyl Tosylates Containing Ortho-Methyl Groups. Inconsistency between Theoretical Calculations and Experimental Results

Solvolyses of tosylates IIB and IIC in a variety of solvents were found to give excellent linear log k -Y_BnOTs plots (R = 0.997 and SD = 0.022) and negative ΔS^≠ for IIB , but slight deviations (R = 0.987 and SD = 0.047) from lineation and positive ΔS^≠ for several cases for IIC . Limiting S_N1 mechanisms with steric hindrance to resonance and solvent intervention at the cationic transition state could thus be confirmed. The inconsistency between theoretical and observed trend of ΔH^≠ is attributed to the neglect of solvent effect in MO calculations. Deductions linking theoretical calculation and solvolytic experiments should be drawn with caution.     

Fluxional sulfonyl derivatives of troponoids and colchicinoids

In what represents the first examples of fluxional sulfonyl derivatives, the tosyl group in the couple 4-isopropyltropone/6-isopropyltropone (3/4), the tosyl or mesyl groups in the couple colchicine/isocolchicine (5/6 or 7/8), and the tosyl group in the couples of colchicinoids 9/10 and 11/12, were observed to undergo thermally-induced shift between the two tropolone-like oxygen atoms, likely via a bipyramidal intermediate; recycling of tosylates or mesylates of biologically inactive isocolchicinoids into the corresponding tosylates or mesylates of biologically active colchicinoids affords synthetic value to the unselective tosylation or mesylation of colchiceine.     

Triton-B Catalyzed, Efficient, One-Pot Synthesis of Carbamate Esters from Alcoholic Tosylates

Summary. A novel process for the one-step chemoselective conversion of a variety of alcoholic tosylates into carbamates serving as protected amines was developed using benzyltrimethylammonium hydroxide (Triton-B) in the presence of gaseous carbon dioxide. Thus carbamate esters of different amines were prepared in very good to excellent yields. Present address: Institute of Organic and Biomolecular Chemistry, Georg-August University, D-37077, G?ttingen, Germany     

Positioning solvolyses within the SN2‐SN1 and SN3‐SN2 spectrum of reaction mechanisms

A simple linear regression (Q equation) is devised to position solvolyses within the established S_N2‐S_N1 spectrum of solvolysis mechanisms. Using 2‐adamantyl tosylate as the S_N1 model and methyl tosylate as the S_N2 model, the equation is applied to solvolyses of ethyl, allyl, secondary alkyl and a range of substituted benzyl and benzoyl tosylates. Using 1‐adamantyl chloride as the S_N1 model and methyl tosylate as the S_N2 model, the equation is applied to solvolyses of substituted benzoyl chlorides in weakly nucleophilic media. In some instances, direct correlations with methyl tosylate were employed. Grunwald–Winstein l values and kinetic solvent isotope effects are also used to locate solvolyses within the spectrum of mechanisms. Product selectivities (S) for solvolyses at 50 °C of p‐nitrobenzyl tosylate in binary mixtures of alcohol–water and of alcohol–ethanol for five alcohols (methanol, ethanol, 1‐propanol and 2‐propanol and t‐butanol) are reported and show the expected order of solvent nucleophilicity (RCH₂OH > R₂CHOH > R₃COH). The data support the original assignments establishing the N_OTs scale of solvent nucleophilicity. Copyright © 2016 John Wiley & Sons, Ltd.     

Arylation of Acrylamide and Acrylonitrile with Arenediazonium Salts Catalyzed by Palladium Acetate

In recent years, palladium catalyzed arylation of olefins, the Heck reaction, has evolved as a powerful synthetic tool for organic chemists1. Since its discovery in the early seventies2, the reaction has undergone several modifications especially with regard to solvents, catalysts and additives. As a result, today Heck reaction is the most widely used transition metal catalyzed carbon-carbon bond forming reaction in organic synthesis3. However, despite all these modifications, little atten…     

Magnetically recyclable Cu-BTC@Fe3O4-catalyzed synthesis of aryl α-chlorobenzyl ketones

Metal–organic framework (MOF) composite, viz. Cu-BTC@Fe₃O₄ (BTC is 1,3,5-benzenetricarboxylate), was prepared and utilized for the synthesis of aryl α-chlorobenzyl ketones from arenediazonium salts and arylacetylenes in moderate to good yields. This reaction proceeded via a radical domino process. The catalyst could be readily recovered with an external permanent magnet, with slight decrease in its activity after successive six runs.