The regioselectivity in the Diels-Alder reactions of styrene with certain substituted 1,4-naphthoquinones was explored. The results were consistent with predictions based upon analysis of dione polarization. We have extended the general Diels-Alder reactions between styrenes and naphthoquinones that were used to prepare l-,2-,3-and 4-halo' and methoxy2 benz[a]anthracene-7,12-diones (BADs) by preparing BADs substituted in the D ring3 (8-,9-,10-and 11-positions). Treatment of 5-hydroxy-1,4_naphthoquinone (,j) with excess styrene and chloranil afforded a mixture of 8-hydroxybenz[a]anthracene-7,12-dione (5) and 11-hydroxybenz[a]anthracene-7,12-dione (2). A similar reaction between 6-methoxy-1,4-naphthoquinone4 (3) and styrene gave a mixture of the g-methoxy (2) and the lo-methoxy (6) isomers. The relative amounts of these products were consistent with predictions derived from a rationale put forth by Kelly5 concerning the Diels-Alder reactions of substituted butadienes with naphthoquinones. Analysis of 5-methoxy-1,4-naphthoquinone' (4) using the model suggested that resonance effects as shown below would furnish C-3 as the more electronegative reaction site. This C"3 would promote formation of 8-methoxybenz[a]anthracene-7,12-dione (2) instead of the llmethoxy isomer (l&l). When compound 1 was heated in toluene solution with chloranil and excess styrene at 110-120Β°C for 9 days 2, mp 189-19O'C (lit8 mp 184-185Β°C) and lt, mp 200.5-202"~ (lit' mp 195Β°C) were isolated by column chromatography, as above, in about a 3.5:1 ratio in 48% yield. This, again, was consistent with prediction. In an attempt to reduce reaction time, trichloroacetic acid (TCA) was added to the styrene-quinone mixtures. The catalytic effect of this acid upon Oiels-Alder reactions was demonstrated by Wasserman' in his studies concerning the cycloadditions of cyclopentadiene to various quinones. In these studies the catalyst not only reduced reaction times 30 to 50%, but also affected isomer distribution and overall yield in the case of the formation of 2 and 2 from 1. Addition of TCA under the conditions stated earlier afforded 2 and 2 in a 3:l ratio in 74; overall yield. An explanation of this effect should include the Wasserman observation from kinetic studies that the primary step in the catalysis is of the third order. This suggests association of the quinone with TCA at or near the transition state. The nature of the association remains speculative. Compared with the butadienes used by Kelly, the poorer diene styrene did not affect the relative reactivity of the various naphthoquinones5. Juglone was by far the most reactive quinone, with compounds l,,Q, and 3 following, in decreasing order. Although the formation of the BADs requires two oxidation subsequent to Diels-Alder adduct formation, our studies have shown that the adduct formation is rate-limiting. 10 Recent work by Boeckman, et al 11 suggested that when various butadienes reacted with 1, 2, and ,8, a large Portion of the regioselectivity observed could be attributed to the particular polarization of the diene. Although styrene may confer a large portion of the regioselectivity when reacting with j,,l, and 8, this quality is not strong enough to effect similar isomer distribution when styrene reacts with 3. Acknowledgements: The author is grateful to Dr. D.J. Wilbur for taking pmr spectra and Mr. S.S. Huang for determining mass spectra.