Reactions of guaiazulene with 2-furaldehyde, thiophene-2-carbaldehyde and pyrrole-2-carbaldehyde in methanol in the presence of hexafluorophosphoric acid: comparative studies on molecular structures and spectroscopic, chemical and electrochemical properties of monocarbocations stabilized by 3-guaiazulenyl and 2-furyl (or 2-thienyl or 2-pyrrolyl) groups

Abstract Reactions of guaiazulene ( 1 ) with heteroaromatic-carbaldehydes [i.e., 2-furaldehyde ( 2 ), thiophene-2-carbaldehyde ( 3 ) and pyrrole-2-carbaldehyde ( 4 )] in methanol in the presence of hexafluorophosphoric acid at 25 °C for 30 min under aerobic conditions give (2-furyl)(3-guaiazulenyl)methylium hexafluorophosphate ( 5 ), (3-guaiazulenyl)(2-thienyl)methylium hexafluorophosphate ( 6 ) and (3-guaiazulenyl)(2-pyrrolyl)methylium hexafluorophosphate ( 7 ), respectively, in 93, 98 and 85% yields. Comparative studies on the molecular structures as well as the spectroscopic, chemical and electrochemical properties of the methylium hexafluorophosphates 5 – 7 stabilized by 3-guaiazulenyl and 2-furyl (or 2-thienyl or 2-pyrrolyl) groups are reported.