942 zyxwvutsrqpon J.C.S. CHEM. COMM., 1981 zy Regiospecific Cycloaddition of 1 -Substituted Isobenzofurans to Quinone Acetals By RONALD N. WARRENER* and BRENDON C. HAMMER (Chemistry Department, Australian National University, zyxwvu P.O. Box 4, Canberra, A .C. T. 2600, Australia) and RICHARD A. RUSSELL* (Chemistry Department, Faculty zyxwvut of Military Studies, University of zyxwvutsrq N.S. W., Duntroon, A .C.T. 2600, Australia) Summary The cycloaddition reaction of 1-substituted iso- benzofurans to quinone acetals is highly stereo-, site-, and regio-specific; the degree of regiocontrol is main- tained over a wide range of substituents. 0 QUINONES enter into cycloaddition reactions with dienes, but the regiospecificity may vary upon changing the substituent on either partner.lY2 Thus reaction of the chloromethylbenzoquinone (2) with 1-bromoisobenzofuran (lc) yields syn-regioisomers of type A zyxwvuts (3) ;3 on the other hand 1-trimethylsilylisobenzofuran yields the anti-regioisomers of type B (4).3 Clearly each reaction is regiospecific, but the reaction lacks the necessary control where type A or type B adducts can be generated on demand (regiocontrol). Quinone acetals have recently emerged as versatile reagents in organic synthesis4v5 and good methods for their preparation are available.* While interest has concentrated on anionic and carbanionic addition to these reagents, we show here that they are valuable dien~philes,~J which react with 1-substituted isobenzofurans in a regiocontrollad fashion.9 In this way type A or type B substitution can be obtained by judicious location of the R3/R4 substituent on the dienone e.g. (5a-d). Transfer of this site location to the adduct is assured since a single product is formed in the cycloaddition reaction,lo irrespective of the nature of the I-substituent on the isobenzofuran. In all cases the (1) a; R'= H b; R'= Me d; R1 zyxwvuts = SiMe3 e; R' = Br f ; R' = C02Me C; R' = CHzOH (4) (3) type 6 zyxwv (anti Me/R') type A (syn MeIR') regioisomer with general structure (6), i.e. with the R1- substituent of the isobenzofuran having a syn-relationship with the carbonyl group of the dienone, is obtained. Published on 01 January 1981. Downloaded by University of Alberta on 26/10/2014 22:24:16. View Article Online / Journal Homepage / Table of Contents for this issue