Solventless synthesis of quaterphenyls and terphenyls under phase transfer catalysis conditions

A more practical approach to terphenyls has been realized by a few direct procedures capable of generating the central benzene ring with a single reaction involving easily available reagents. For example, a mixture of meta-terphenyl 3a (50% yield) along with sulfonyl-meta-terphenyl 5a (36% yield) has been obtained by reacting allylsulfone 1a with chalcone 2a in the presence of excess of NaH in THF at 50 °C (Scheme 1).1 By the same approach, 1,2,4-quaterphenyls 4a can also be obtained by using an aryl substituted allyl sulfone 1b.In order to develop a more practical approach and increase the selectivity, we planned to carry out this reaction under phase transfer catalysis (PTC) conditions. In fact, PTC represents a powerful tool to replace hazardous and relatively expensive reactants such as NaH with cheap and practical bases such as alkaline carbonates and hydroxides. In addition, mild reaction conditions, safety, operational simplicity, and high selectivity are widely accepted typical features of PTC processes that allow an easy scale-up of reactions. The best results have been obtained by heating at 70 °C for 1 h equimolar amounts of allylsulfones 1 and chalcones 2 in the presence of solid NaOH (4 eq) and PEG 1000 (0.4 eq) as phase transfer catalyst. No additional solvent is required to ensure fast conversion of the reactants in a short time.