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

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(1 H )‐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(1 H )‐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.