Regioselective syntheses of 6-(1,1-dimethylallyl)- and 8-(3,3-dimethylallyl) chrysins

The first regioselective syntheses of 6-(1,1-dimethylallyl)- and 8-(3,3-dimethylallyl) chrysins have been designed. Claisen rearrangement of protected 5-O-(3,3-dimethylallyl) chrysin in N,N-diethylaniline at 200–217°C gave selective access to the 8-(3,3-dimethylallyl) isomer. Similar rearrangement in N,N-diethylbutylamine at 140–160°C, or in cycloheptane/Eu(fod)3 at 100°C, led to the formation of the 6-(1,1-dimethylallyl) isomer. Four different protecting groups for position 7 of chrysin have been compared, and found to follow the order of interest Bz>MOM>TBDPS>MEM.