Synthesis of substituted 2-aroyl-3-methylchromen-4-ones from isovanillin via 2-aroyl-3-methylchroman intermediates

Isomerization of Allylbenzenes

“…Wang and co-workers readily isomerized 2-(2-allyl-3,4-dimethoxyphenoxy)-1-(4-chlorophenyl)­ethanone 151 with 1 equiv of potassium tert -butoxide at 0 °C, to afford the substituted styrene derivative 152 . When the reaction was performed with 2 equiv of potassium tert -butoxide in tetrahydrofuran at reflux, the cyclized product 153 was obtained as a mixture of cis - and trans -diastereoisomers (29% and 50%, respectively) (Scheme ).…”

“…303 Wang and co-workers readily isomerized 2-(2-allyl- equiv of potassium tert-butoxide at 0 °C, to afford the substituted styrene derivative 152. 304 When the reaction was performed with 2 equiv of potassium tert-butoxide in tetrahydrofuran at reflux, the cyclized product 153 was obtained as a mixture of cis-and trans-diastereoisomers (29% and 50%, respectively) (Scheme 33). The authors proposed that products 153 were formed by what was described as an "intramolecular carbanion-olefinic 6-endo-trig cyclization".…”

Addition of Metal Enolate Derivatives to Unactivated Carbon−Carbon Multiple Bonds

“…Very recently, t BuOK was found to promote the cyclization of 2-allyl-phenoxy-1-aroylethanone derivatives (Scheme ) . While the use of only 1 equiv of t BuOK at 0 °C in tetrahydrofuran (THF) resulted in the migration of the carbon−carbon double bond into the benzylic position, 6- endo -cyclization took place in the presence of a 2-fold excess of t BuOK in refluxing THF.…”