The chemistry of 2H‐3,1‐benzoxazine‐2,4(1H)‐dione (isatoic anhydride). 10. Reactions with ester enolates. Synthesis of 4‐hydroxy‐1‐methyl‐3‐prenyl‐2(1H)‐quinolinones, Crucial intermediates in the synthesis of quinoline alkaloids

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Abstract
N‐Methylisatoic anhydride reacts with the lithium enolates of esters to produce β‐ketoesters 4 in nearly quantitative yield. Thermal cyclization of these relatively unstable intermediates afford the corresponding 3‐substituted‐4‐hydroxy‐1‐methyl‐2(1H)‐quinolinones (5) in good yields. The reaction of the lithium enolate of 5‐methyl‐4‐hexenoic acid ethyl ester (14) with various nuclear substituted isatoic anhydrides gives 4‐hydroxyl‐methyl‐3‐prenyl‐2(1H)‐quinolinones 8, 9, and 18 which are highly desirable intermediates in the synthesis of a variety of quinoline alkaloids. Treatment of 18 with DDQ furnishes oricine in 73% yield.