High-yield catalytic metathesis of alkenyl tosylates with applications in organic synthesis

Alkenyl tosylates of the type RCHCH(CH₂)_nOTs [RH, n=9; RH, n=7; and RCH₃(CH₂)₇, n=8] undergo metathesis using a WCl₆-Me₃SnCl catalyst system, producing difunctionalised alkenes of the type TsO(CH₂)_nCHCH(CH₂)_nOTs (n=7,8, and 9); examples of the use of these products in synthesis are presented.     

Organocatalysis as a safe practical method for the stereospecific dibromination of unsaturated compounds

Organocatalytic stereospecific dibromination of a wide variety of functionalized alkenes was achieved using a stable, inexpensive halogen source, 1,3-dibromo 5,5-dimethylhydantoin, and a simple thiourea catalyst at room temperature. The presence of a tertiary amine enhanced the rate of the dibromination reaction, and yields were good in various solvents, including aqueous solvents. The procedure was extended to alkynes and aromatic rings and to dichlorination reactions by using the 1,3-dichloro hydantoin derivative.     

Solvent-free synthesis of unsaturated amino esters in a ball-mill

The ball-milling technique was used under solvent-free conditions to perform a Horner-Wadsworth-Emmons reaction in the presence of a mild carbonate base. Starting from a phosphonate-substituted glycine, this method gave access to Boc-protected unsaturated amino esters in excellent yield and selectivity in many cases. The scope of the reaction was delineated.     

Enantioselective synthesis of unsaturated amino acids using p-methoxybenzylamine as an ammonia equivalent

A versatile, non-alkylative enantioselective synthesis of unsaturated α-amino acids based on the Sharpless asymmetric epoxidation has been developed. Enantiomerically enriched trans epoxy alcohols bearing unsaturated substituents were prepared and submitted to regio- and stereospecific ring-opening with p-methoxybenzylamine as a nucleophile, leading to anti-3-(p-methoxybenzylamino)-1,2-diols which were further protected by reaction with Boc₂O. The 1,2-diol fragment was then oxidatively cleaved by a sequential treatment with sodium periodate and sodium chlorite to afford the corresponding amino acid. Using this methodology, doubly N-protected (p-methoxybenzyl and Boc) allyl glycine, 3-butenyl glycine and 4-pentenyl glycine have been prepared in three synthetic steps from the corresponding allyl alcohols. As a demonstration of the orthogonal nature of the nitrogen protection, both protecting groups have been selectively removed from the fully protected amino ester.     

Enol tosylates as viable partners in Pd-catalyzed cross-coupling reactions

[reaction: see text] Herein we demonstrate functionalized enol tosylates to be robust substrates that undergo Suzuki-Miyaura, Sonogashira, and Stille cross-coupling reactions to provide stereodefined trisubstituted unsaturated esters.     

A new one-pot solvent-free synthesis of pyridinyl tosylates via diazotization of aminopyridines

A new, convenient, one-pot method for the synthesis of pyridinyl tosylates is developed. The procedure involves sequential diazotization/tosylation of aminopyridines with sodium nitrite and p-toluenesulfonic acid under solvent-free conditions in a water paste at room temperature.     

Modification of unsaturated rubbers in low-temperature plasma as a method to improve their adhesion properties

The change in the contact-surface properties of the films of unsaturated rubbers under the effect of a direct-current discharge has been investigated in case of the placement of the samples at the anode. It has been demonstrated that the modification in plasma leads to a substantial improvement in the contact properties of rubber films.     

Claisen amino rearrangement as a method for synthesis of C-cycloalkenylanilines

Conclusions The reaction of 3-chlorocycloalkenes with excess aromatic amine leads to o-(2-cycloalkenyl)-substituted aromatic amines.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2160–2162, September, 1982.     

Facile synthesis of unsaturated pyroglutaminol derivatives

A novel approach to the synthesis of unsaturated pyroglutaminol derivatives was developed. Condensation of a protected serine derivative with Meldrum’s acid followed by decarboxylative cyclization afforded a tetramic acid, which was then converted to a hydroxylactam using sodium borohydride. Iodine displacement of the hydroxyl group induced spontaneous elimination to afford unsaturated pyroglutaminol derivatives in good yields.     

A new synthesis of unsaturated aldehydes

Treatment of 3-trimethylsilylallylic alcohols with phenylsulphenyl chloride gives unstable allylic sulphoxides which rearrange and are then hydrolysed to unsaturated aldehydes.     

An alternative synthesis of unsaturated aldehydopheromones

The pheromone 7(Z)-tetradecenal and its isomer 7 (E)-tetradecenal were synthesized in four steps from commercially available starting materials.     

Arm-first method as a simple and general method for synthesis of miktoarm star copolymers

Miktoarm star copolymers containing two or more arm species were synthesized by atom transfer radical polymerization using a simple and general "arm-first" method, that is, one-pot cross-linking a mixture of different linear macroinitiator (MI) species by a divinyl cross-linker, such as divinylbenzene. Using linear MIs with a high degree of bromine chain-end functionality, including polyacrylate, polystyrene, polymethacrylate and poly(ethylene oxide), resulted in high-yield star polymers (>90%). Characterized by liquid adsorption chromatography techniques, which separated star polymers on the basis of the chemical composition of arms, the obtained star product was proved to be miktoarm star copolymers containing two or more arm species in one molecule, instead of mixture of different homoarm star polymers. Within our investigation, the molar ratios of the arms in the miktoarm star copolymers were always in agreement with the composition of the initial MI mixture, indicating the powerful capacity of this arm-first method for synthesis of miktoarm star copolymers with potentially any molar ratios and species of the arms. By using a mixture containing five types of linear MIs with different chemical compositions, miktoarm star copolymers containing five kinds of arms were synthesized for the first time, which significantly expanded the methodologies for synthesis of miktoarm star copolymers by living polymerization techniques.     

Nucleophilic cyclizations of enediynes as a method for polynuclear heterocycle synthesis

In this review, data on the heterocyclization of enediynes, initiated by attack of an external anionic nucleophile or a nucleophilic group present in the molecule at the C ≡ C bond of the enediyne, are summarized.     

Intramolecular photocycloaddition of cyclic thioimides as a method for heterocyclic synthesis

Cyclic thioimides undergo photocycloaddition with tethered pi-bonds in a regiospecific manner to afford spirocyclic amidothietanes. These highly strained multicycles undergo a subsequent ring opening reaction to furnish novel fused pyrrolizinones.