Reactivity of pyridines bearing EWG with bis-(TMS)ketene acetals. Substituent-induced lactonization reaction

One-Pot Synthesis of Spirotetrahydrooxino[3,4-c]pyridines and Spirotetrahydrofuro[3,2-b]pyridin-2-ones via Lactonization from Activated Pyridyldihydroozaxoles and Bis(trimethylsilyl)ketene Acetals

“…12 In related reports, a mixture of 2 and 4-addition products were obtained. 30 In contrast to the previously reported study by our group, in which the activated 4-R-substituted pyridines (R = CN, CO 2 Et, COH) reacted with ketene acetals to give addition exclusively at the 4-position, 11 in the present study the addition occurred regioselectively at position 2 to yield the products 19a,a′ and 21a.…”

“…This is carried out via a nucleophilic addition of bis(trimethylsilyl)ketene acetals over a variety of different substrates such as acetylenic ketones, pyridines, imidazoles, allylic derivatives activated by Lewis acids, triflic anhydride, methyl chloroformate, and a palladium complex. [10][11][12][13] The spirolactone structure is also important for the present study. Spiroorthocarbonates (SOCs) and related compounds have received a great deal of attention as monomers since they polymerize without any shrinkage in volume.…”

Rearomatization of trifluoromethyl sulfonyl dihydropyridines: Thermolysis vs photolysis

“…Pure compounds 9 and 10 were prepared as previously reported and together with main products were characterized by standard spectroscopic techniques ( 1 H, 13 C, 19 F, and UV) and mass spectrometry. All data are in agreement with the proposed structures.…”

Reactions of Bis(trimethylsilyl)ketene Acetals with Several Activated Organic Substrates

“…When 2‐substituted pyridines 45 and 46 , bearing electron‐withdrawing groups, are activated with triflic anhydride to give compounds 47 , nucleophilic addition of 1 and subsequent hydrolysis leads in the first instance to the corresponding dihydropyridinecarboxylic acids 49 and 50 , Scheme …”

“…[21] When 2-substituted pyridines 45 and 46, bearing electronwithdrawing groups, are activated with triflic anhydride to give compounds 47, nucleophilic addition of 1 and subsequent hydrolysis leads in the first instance to the corresponding dihydropyridinecarboxylic acids 49 and 50, Scheme 16. [22] These acids can be efficiently turned into new bicyclic γlactones 51 and 52 through an unprecedented silica-gelassisted Michael-type ring closing procedure through intramolecular 1,4-addition of the carboxylic acid in the 4-position to the -carbon of the conjugated system R-Cα=C , in which the Michael reaction is favored by the presence of the electronwithdrawing groups in the 2-position and the acidic character of the silica gel.…”