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A direct and regioselective synthesis of p-phenylthio-substituted peri-hydroxy polyaromatic compounds (9-12) was developed via the strong-base-induced [4+2] cycloaddition of the 4-(phenylthio)homophthalic anhydrides (1a-d) to the phenylsulfinyl-substituted dienophiles (5-8). The sulfinyl group in 5-8 is the key to producing the desired reaction under mild conditions (at -20 °C to room temperature) in good yields. A reaction mechanism explaining the remarkable effect of the sulfinyl group is discussed.

An Efficient Synthesis of peri-Hydroxy Aromatic Compounds: A Strong Base-Induced [4 + 2] Cycloaddition of 4-Phenylthio-Substituted Homophthalic Anhydrides with Various Sulfinyl-Substituted Dienophiles.-In the presence of strong base, the 4-phenylthio-homophthalic anhydride derivative (I) readily reacts with dipolarophiles such as the acetylenedicarboxylic acid ester (II) to give the desired [4 + 2] cycloadducts. However, the reaction with quinones such as (IV) requires a long reaction time and gives the p-phenylthio substituted peri-hydroxy aromatic compounds (V) in low yield. In contrast, the sulfinyl-substituted dienophiles (VI) react almost immediately at room temp. to give the desired products (V). Application of this anionic cycloaddition to dienophile (VII) allows an access to the ABCD-ring analogue (IX) of fredericamycin A. -(KITA, Y.; IIO, K.; OKAJIMA, A.; TAKEDA, Y.; KAWAGUCHI, K.; WHELAN, B. A.; AKAI, S.; Synlett (1998) 3, 292-294; Fac. Pharm. Sci.,