A Facile Synthesis and Ring-Opening Reactions of Novel 2-Ferrocenyl-3,4-dihydropyrans

A series of novel 2-ferrocenyl-3,4-dihydropyrans were synthesized in good to excellent yields through three-component reaction of vinylferrocene, 1,3-dicarbonyl compound and formaldehyde near room temperature under catalyst-free conditions.The obtained ferrocenyl dihydropyrans can also react readily with indole in the presence of alum, providing a ring-opening product in high yield, and this result opens an effective way to access a new class of complex ferrocenyl derivatives.Recently, there has been a resurgence of interest in the synthesis and design of ferrocenyl derivatives because of their wide-spread applications in material chemistry, 1,2 asymmetric catalysis, 3 and bioorganometallic chemistry 4 and so on. 5Of course, the design motif and synthesis strategy for ferrocenyl-based architectures play the most important roles in delivering the required properties.Although ferrocenyl derivatives are classical aromatic compounds, traditional methods for the constructing aromatic compounds may not work for ferrocene due to its specific geometric and electronic properties. 6Furthermore, ferrocenyl fragments are sometimes sensitive to acid and high temperature. 7erefore, developing efficient methods for their synthesis under mild reaction conditions remains to be a challenge.Multicomponent reactions (MCRs) have become a promising tool for synthetic organic chemists, since they allow complicated molecules to be created using one reaction in a fast, efficient, simple and energy savings manner. 8Gu and Jérȏme 9 reported a simple method for the synthesis of 2-aryl-3,4-dihydropyrans through multicomponent reaction of formaldehyde, 1,3-dicarbonyl compound and styrene.The key of this MCR is generation and the following trapping of a 2-methylene-1,3-dicarbonyl intermediate with styrene.According to a recent report of Cavaleiro, 10 β-vinyl-meso-tetraphenylporphyrin can also trap this type