The Condensation of Paraformaldehyde with Aromatic Ketones

Superacid-Catalyzed Electrocyclization of 1-Phenyl-2-propen-1-ones to 1-Indanones. Kinetic and Theoretical Studies of Electrocyclization of Oxonium−Carbenium Dications

“…Another related cyclization of 3-hydroxy-2-methyl-1-phenylpropan-1-one 5 (R 2 = H, R 3 = CH 3 ) to give 3-methylindanone ( 2g ), catalyzed by concentrated sulfuric acid, was also reported …”

“…A related cyclization of 2-methyl- ( 1g ) and 2-ethyl-1-phenyl-2-propen-1-ones ( 1h ) was previously studied, the reaction being catalyzed by concentrated sulfuric acid (88% yield of 2g ; 49% yield of 2h ). TFSA catalyzes these cyclization reactions of 1g and 1h more efficiently than sulfuric acid to give indanones (both in 97% yield at 25 °C for 2 h).…”

“…Phenyl vinyl ketones, wherein one of the phenyl groups of benzophenone is replaced with an olefin, are thus of interest as potential substrates for cyclization. Some previous studies of relevant cyclization reactions have been reported. − Acid-catalyzed cyclization reaction of naphthalenyl vinyl ketones to give benzoindanone derivatives was described as early as 1927: 5 the reaction required drastic conditions, such as heating on a steam bath in concentrated sulfuric acid. Related cyclizations of 1-benzoyl-1-cyclohexene 6 and 1-benzoyl-1-cycloheptene 7 were also reported, and also required strongly acidic conditions, such as a mixture of phosphoric acid and phosphorus pentoxide (equivalent to polyphosphoric acid) with heating on a steam bath or a mixture of phosphoric acid and formic acid at 90 °C.…”

“…Related cyclizations of 1-benzoyl-1-cyclohexene 6 and 1-benzoyl-1-cycloheptene 7 were also reported, and also required strongly acidic conditions, such as a mixture of phosphoric acid and phosphorus pentoxide (equivalent to polyphosphoric acid) with heating on a steam bath or a mixture of phosphoric acid and formic acid at 90 °C. The prototype cyclization of 1-phenyl-2-propen-1-ones, in particular of 2-methyl- ( 1g ) and 2-ethyl-1-phenyl-2-propen-1-ones ( 1h ) was previously investigated, and was found to be catalyzed by concentrated sulfuric acid. Cyclization of 1,2-diaryl-2-propen-1-ones with multiple substituents on the aromatic rings was also reported to be catalyzed by concentrated sulfuric acid .…”

“…The reaction intermediates in the cyclization of 1-phenyl-2-propen-1-ones and related aromatic systems have been little discussed, though a superficial chemical analogy with the Nazarov reactions led to the suggestion that the electrocyclization reaction involves the O -protonated phenyl vinyl ketones . (2) Although the parent 1-phenyl-2-propen-1-one is known, , it has not been established whether or not the prototype electrocyclization of this compound takes place. A substituent at the 2-position of 1-phenyl-2-propen-1-ones seems to be relevant to the cyclization, because the reported examples of the cyclization are limited to 2-substituted 1-phenyl-2-propen-1-one derivatives such as 1-benzoyl-1-cyclohexene.…”