INTRAMOLECULAR HECK REACTION FOR THE SYNTHESIS OF ISOCHROMANES UNDER AMBIENT AND HIGH-PRESSURE

The iodoarenes 9 and 10, bearing (E)- and (Z)-alkene moieties, respect ively, easily prepared by alkylation of the corresponding alcohols 7a- c and 8a-c with 2 iodobenzyl iodide, undergo intramolecular Heck react ions to give the isochromanes 12-15a-c in good yields. The selectivity of the reaction depends on the size of the substituent R in 9 and 10; increasing bulkiness of R leads to a decrease in diastereoselectivity and an increase in regioselectivity. High-pressure experiments confir m the proposed mechanism and show that bromoarenes such as 11, which t end to be unreactive at ambient pressure, give good results when the c yclisation is performed under high pressure.