Synthesis of 2-trifluoromethoxyethyl trifluoromethoxyacetate and derived 2-trifluoromethoxyacrylates

The synthesis of 2-trifluoromethoxyethyl trifluoromethoxyacetate 2 by oxidation of bis(2-trifluoromethoxyethyl)ether 1 followed by its anionic condensation with aldehydes, ketones and immonium salts under mild conditions, and further dehydration or deamination, enabled the preparation of 3-aryl and 3-alkyl-2-trifluoromethoxacrylates 8a-e as well as the parent 2-trifluoromethoxyacrylate 8f.     

Formation of 3-[amino(aryl)-methylidene]-1,3-dihydro-2H-indol-2-ones involving ring transformation of 2-aryl-5-(2-aminophenyl)-4-hydroxy-1,3-thiazoles

The reaction of 3-bromooxindole with substituted (hetero)aromatic thioamides in acetonitrile was studied. At room temperature the reaction preferably gives products of ring transformation i.e. 2-aryl-5-(2-aminophenyl)-4-hydroxy-1,3-thiazoles (3b-f,h) whereas at elevated temperature products of an Eschenmoser coupling reaction, i.e. 3-[amino(aryl)-methylidene]-1,3-dihydro-2H-indol-2-ones (2b-f), are formed exclusively. There exist only two exceptions (4-methoxy and 2-pyridinthioamide) in which the Eschenmoser coupling reaction always takes place giving 2a and 2g. Also N-methylation of the starting 3-bromooxindole completely prevents formation of thiazoles. The prepared thiazoles 3b-f are unstable in solution and they undergo slow ring transformation to 2b-f. The rate limiting step of this rearrangement involves cleavage of an intermediary thiirane ring, which is slowed down by electron-withdrawing substituents on the thioamide (ρ = ?1.15).     

The influence of the ring size of thiolactams in the Eschenmoser coupling reaction in presence of DBU. Formation of bicyclic thiazolidinones or thioimines

The different behaviors of pyrrolidin-2-thione and piperidin-2-thione under a modified Eschenmoser sulfur contraction reaction protocol using DBU as base was observed. The pyrrolidin-2-thione 1b follows the expected reaction course, leading to thioimines 5a-d, which can be transformed subsequently into the respective by action of a thiophile, while the piperidin-2-thione leads to the formation of bicyclic thiazolidinones 4b-d in moderate to good yields. The β-enaminocarbonyl compound 11 was hydrogenated to afford the respective five-membered analogue of methylphenidate 12.     

Facile conversion of Biginelli 3,4-dihydropyrimidin-2(1H)-thiones to 2-(2-hydroxy-2-arylvinyl) dihydropyrimidines via Eschenmoser coupling

A one-pot, two-step synthesis protocol for the conversion of Biginelli 3,4-dihydropyrimidin-2(1H)-thiones to 2-(2-hydroxy-2-arylvinyl) dihydropyrimidine (DHPM) derivatives via Eschenmoser sulfide contraction coupling is described. Solution phase as well as solid-supported protocol was carried out for the decoration of the Biginelli DHMP scaffold at the C-2 position. The scope of the optimized protocol is demonstrated for different DHMP precursors.     

Synthesis of an external beta-turn based on the GLDV motif of cell adhesion proteins

The (3S,6S,10S)-7/5 bicyclic lactam 8, designed as an external turn constraint, was synthesised by a new stereoselective route involving Eschenmoser condensation. The cyclic peptide 35 containing the integrin recognition motif GLDV added across the amino and carboxyl groups of the lactam external constraint 8 was prepared.     

A study of the Claisen—Eschenmoser reaction for hydroxymethylbenzofurans and-indoles

N,N-Dimethylacetamide dimethyl acetal reacted with 5(7)-substituted 2-(hydroxy-methyl)benzofurans to give N,N-dimethyl-2-(2-methylbenzofuran-3-yl)acetamides. Analogous reactions with 3-(hydroxymethyl)indole and 1-hydroxy-6-methyl-1,2,3,4-tetrahydro-carbazole afforded N,N-dimethyl-3-(3-indolyl)propionamide and N, N-dimethyl-2-(6-methyl-1,2,3,4-tetrahydrocarbazol-1-yl)acetamide, respectively. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 314–318, February, 2007.     

Tetra-n-butylammonium Fluoride–Catalyzed Eschenmoser–Claisen [3,3]-Sigmatropic Rearrangement

Condensation of dibenzofuran and dibenzothiophene carboxaldehydes with various aryl acetic acids followed by esterification of the acid intermediate afforded the 2,3-diaryl acrylates in good overall yields. Reduction of the esters with diisobutylaluminium hydride afforded the allylic alcohols, which underwent a smooth Eschenmoser–Claisen [3,3]-sigmatropic rearrangement on exposure to N,N-dimethylacetamide dimethylacetal in the presence of tetra n-butylammonium fluoride as catalyst to give 3,4-diaryl γ,δ-unstaturated amides in excellent yields.