Synthesis of Highly Substituted Biaryls by the Construction of a Benzene Ring via In Situ Formed Acetals

Silver-Catalyzed Olefination of Aryl Aldehydes Using Propiolates

Olefination of aldehydes is one of the fundamental reactions in organic synthesis. The commonly used Wittig olefination reaction however uses stoichiometric quantities reagents under basic conditions resulting in stoichiometric amounts of byproducts. Known catalytic alternate to the Wittig reaction requires stoichiometric amounts of silane reducing agents and high temperature. Herein, we report a base-free olefination of aryl aldehydes using propiolates as a surrogate for the Witting reagent under silver catalysis. Trimethyl orthoformate, in the presence of a silver catalyst adds to the alkynoate to form the nucleophilic silver allenolate which reacts with the reactive oxocarbenium ion formed from aldehyde under the reaction conditions. Subsequently, decarbonylation occurs to form the olefin. Trans olefin is formed exclusively from simple aryl aldehydes and cinnamaldehydes. Such a silver allenolate is conceptually novel and has not been explored so far.

Ag(I)-catalyzed cyclization of o-alkynylacetophenones facilitated through acetal formation: synthesis of C3-naphthyl indole derivatives

A mild method for an efficient synthesis of C3-naphthyl indoles from o-alkynylacetophenones has been developed. This Ag-catalyzed transformation is assisted by the acetal formed under the reaction condition employing trimethyl orthoformate (TMOF). The role of acetal in promoting the reaction under ambient conditions has been established with control experiments. A range of C3-naphthyl indole derivatives have been synthesized in moderate to very good yields.

Rearrangement of Methylenebis(cyclohexane-1,3-dione) Enols Induced by Mn(III)-Catalyzed Aerobic Oxidation

The Mn(III)-catalyzed aerobic oxidation of methylenebis(cyclohexane-1,3-dione) enols 1 resulted in 6a-hydroxy-2,3,4,6a,7,8,9,10a-octahydro-1H-benzo[c]chromene-1,6,10-triones 3 during the formation of 4,5,8,10,11,12-hexahydro-2H-benzo[b]oxecine-2,6,7,9(3H)-tetraones 2. The mechanism for the formation of 3 was proposed on the basis of the isolation of intermediates 2, which were transformed into 3 under Claisen and retro-Claisen conditions.

Activation of o-Propargyl Alcohol Benzaldehydes under Acetalization Conditions for Intramolecular Electrophile Intercepted Meyer-Schuster Rearrangement

The reactivity of o-propargyl alcohol benzaldehydes has been increased tremendously toward Brønsted acid-catalyzed intramolecular electrophile intercepted Meyer-Schuster (M-S) rearrangement under acetalization conditions using trimethyl orthoformate (TMOF). The in situ formed acetal transfers the methoxy group intramolecularly to generate the M-S intermediate in even less reactive substrates, and the formed oxocarbenium ion makes the carbonyl more electrophilic for an effective intramolecular trapping of the M-S intermediate to furnish the indanone derivatives.