BENZOPYRANS .32. REACTION OF SOME SIMPLE CONDENSATES OF 4-OXO-4H-1-BENZOPYRAN-3-CARBOXALDEHYDES WITH DIAZOMETHANE SYNTHESIS OF HETEROCYCLESLINKED TO 3-POSITION OF [1]BENZOPYRAN
Ck. Ghosh et al., BENZOPYRANS .32. REACTION OF SOME SIMPLE CONDENSATES OF 4-OXO-4H-1-BENZOPYRAN-3-CARBOXALDEHYDES WITH DIAZOMETHANE SYNTHESIS OF HETEROCYCLESLINKED TO 3-POSITION OF [1]BENZOPYRAN, Indian journal of chemistry. Sect. B: organic chemistry, including medical chemistry, 32(6), 1993, pp. 630-636
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 th
e former gives on heating the dihydrofuran (17) whereas compound (11)
obtained from the latter affords the beta-methylated alkene (7). Unlik
e its analogues 2 and 3, the alpha-cyanoacrylic ester (4) on treatment
with diazomethane furnishes the dihydrofuran (18), a stereoisomeric m
ixture 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 alkoxycar
bonylcyclopropane --> 5-alkoxy-2,3-dihydrofuran transformation. When a
lpha-cyanoesters (21-24) are treated with diazomethane, no dihydrofura
ns are indicated.