A convenient one-pot synthesis of 2-(trifluoromethyl)-3,4,7,8-tetrahydro-2H-chromen-5(6H)-one derivatives and their further transformations

Facile Stereoselective Synthesis of Fluorinated Flavanone Derivatives via a One-Pot Tandem Reaction

“…Moreover, a number of electrophilic fluorinating agents with a N−F structure have been employed to introduce the fluorine atom into organic molecules, and the electrophilic fluorination reaction of β-ketoesters with these fluorinating reagents is also well-documented . On the basis of these studies and as a part of our continued interests in the synthesis of fluorinated heterocyclic compounds, we reasoned that fluorinated flavanones may also be accessible through a Knoevenagel condensation/Michael addition/electrophilic fluorination sequence directly from β-ketoesters 1 and aldehydes. Herein, we report our results with this strategy.…”

An Efficient One-Pot Two-Step Three-Component Process for the Synthesis of Trifluoromethylated Hydrochromenes

“…Intramolecular attack of alcoholate from the Si face of the carbonyl group forms six-membered ring to generate the sole diastereoisomer 4. According to the literature, 8,9 the proton attached to oxygen of hydroxyl group may form an intra-molecular H-bond with the oxygen of carbonyl group, which indicates that hydroxyl group and ester group in a cis-axial configuration might be more stable. Thus, the (±)-(2S,3S,4R) relative configuration of 4a is more preferred.…”

“…tal. 9,10,19 In addition, the structure of hemiketal in products 4 is very stable due to the strong electrophilic trifluoromethyl group close to the hydroxy on the six-membered ring. To solve these issues, product 4a was used as the model substrate with some common dehydration catalysts in refluxing anhydrous toluene to screen suitable reaction conditions (Table 3, entries 1-5).…”

“…Among them, there are some new methods for the synthesis of fluorine-containing hexahydro-2H-chromenes by three-component reactions with cyclohexanedione derivatives, substituted benzaldehydes, and fluorine-containing 1,3-dicarbonyl compounds or derivatives. [8][9][10] Although similar methods have been described for many years, so far, a three-component reaction using fluorine-containing acetylene derivatives to regioselectively and diastereoselectively obtain fluorine-containing hexahydro-2H-chromenes has never been reported.…”

Iron(III) Chloride Catalyzed Formation of 3,4-Dihydro-2H-pyrans from α-Alkylated 1,3-Dicarbonyls. Selective Synthesis of α- and β-Lapachone

“…Additionally, prenylated β-ketoester 2 was reported to result in the formation of the corresponding 3,4-dihydro-2 H -pyran product upon treatment with either stoichiometric SnCl 4 or catalytic I 2 , PPh 3 , while the conversion of indanedione 3 in excess sulfuric acid proceeded in only low yields . The majority of current strategies toward 3,4-dihydro-2 H -pyrans ( IV ) rely on cycloaddition reactions of enolizable 1,3-diketones in the presence of superstoichiometric amounts of either a Brønsted or Lewis acid ­(Figure ). Alternatively, 3,4-dihydropyrans can be synthesized via radical cyclization involving an aldehyde and two alkenes .…”