BENZOPYRANS .32. REACTION OF SOME SIMPLE CONDENSATES OF 4-OXO-4H-1-BENZOPYRAN-3-CARBOXALDEHYDES WITH DIAZOMETHANE SYNTHESIS OF HETEROCYCLES LINKED TO 3-POSITION OF [1]BENZOPYRAN

Diazomethane adds to the exocyclic alkenic bond of acrylic esters (2) and (3) (R1=H, Me, and/or Cl); the resultant I-pyrazoline (10) from the former gives on heating the dihydrofuran (17) whereas compound (11) obtained from the latter affords the beta-methylated alkene (7). Unlike its analogues 2 and 3, the alpha-cyanoacrylic ester (4) on treatment with diazomethane furnishes the dihydrofuran (18), a stereoisomeric mixture of cyclopropane (20) and pyrazoline (14). The dihydrofuran (18) on heating at 180-degrees for 30 min followed by chromatography over alumina gives in nearly quantitative yield cyclopropane (20). Thermal rearrangement of 18 to 20 is the first example of a reversed alkoxycarbonylcyclopropane --> 5-alkoxy-2,3-dihydrofuran transformation. When alpha-cyanoesters (21-24) are treated with diazomethane, no dihydrofurans are indicated.