A facile synthetic route to 2 H-chromenes: reconsideration of the mechanism of the DBU-catalyzed reaction between salicylic aldehydes and ethyl 2-methylbuta-2,3-dienoate.
Reactions of salicylaldehydes with ethyl buta-2,3-dienoate or penta-3,4-dien-2-one catalyzed by a catalytic amount of potassium carbonate produce the corresponding 2 H-chromene products in moderate to good yields under mild conditions. A plausible reaction mechanism is discussed in the light of the results of an 18O-labeling experiment. In addition, in view of these findings, the catalytic function of DBU in reactions of this kind is reconsidered.
Dai
Lun-Zhi
LZ
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, China.
Shi
Yong-Ling
YL
Zhao
Gui-Ling
GL
Shi
Min
M
D000447:Aldehydes / Q000737:chemistry*; D001578:Benzopyrans / Q000138:chemical synthesis* / Q000737:chemistry; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000737:chemistry*; D002384:Catalysis; D005231:Fatty Acids, Unsaturated / Q000737:chemistry*; D015394:Molecular Structure; D012459:Salicylates / Q000737:chemistry*
D000447:Aldehydes; D001578:Benzopyrans; D019086:Bridged Bicyclo Compounds, Heterocyclic; D005231:Fatty Acids, Unsaturated; D012459:Salicylates; C521212:ethyl 2-methylbuta-2,3-dienoate; C031033:1,8-diazabicyclo(5.4.0)undec-7-ene