3.3.6.6- TETRAMETHOXY-l ,4-CYCLOHEXADIENE

Hydroquinone dime- 3,3,6,6-Tetramethoxy-l,4-cyclohexadiene (88%) thyl ether... 

Anthracyclinont synthesis. Reaction of 1 with l-lithio-3,3,6,6-tetramethoxy-l,4-cyclohexadiene(7,191) affords the quinone monoketal 3 (70% yield). Similarly, 1 reacts with 4 and 5 to afford 6 (47% yield) and 7 (63% yield), respectively. The mechanism of this transformation is unknown. In any event, 1 functions as an equivalent of the 1,4-dipole 8. 

Antkracyclinones. The use of latent quinone reagents such as 2-lithio-3,3,6,6-tetramethoxy-l,4-cyclohexadiene has been extended to a synthesis of an anthra-cyclinone. The starting material 1 was converted into the quinone bisketal 2 by anodic oxidation. The corresponding lithio compound was then condensed with dimethyl 3-methoxyphthalate (3). The reaction fortunately was stereoselective and resulted in 4 in satisfactory yield. The conversion of 4 to the anthracyclinone 5 was conducted in three steps without isolation of intermediates reductive hydrolysis to the hydroquinone, saponification, and finally cyclization with hydrogen fluoride. The overall yield of 5 from 3-bromo-2,5-dimethoxybenzalde-hyde, the precursor of 1, was 8%. ... 

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