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DOI: 10.1055/s-0029-1220141
Multicomponent Prins-Friedel-Crafts Synthesis of 4-Aryl-5,6-Dihydropyrans
U. C. Reddy, A. K. Saikia*
Indian Institute of Technology, Guwahati, India
Publication History
Publication Date:
22 June 2010 (online)
Significance
Reported is the synthesis of 4-aryl-5,6-dihydropyrans through a Lewis acid mediated multicomponent process. The reaction is proposed to proceed first by nucleophilic attack of the homopropargylic alcohol on the aldehyde to give an intermediate which undergoes Prins cyclization and then Friedel-Crafts reaction with the aromatic solvent. Epoxides could also be used instead of aldehydes, which further increases the scope of this reaction by providing access to substrates that would otherwise require the use of problematic aldehydes. The reaction failed for electron-donating aromatic aldehydes, such as anisaldehyde (rationalized by the increased stability of the benzylic cation intermediate which leads to an oxina-[3,3]-sigmatropic rearrangement). The attempted use of electron-rich aromatics as solvents did not provide useful yields, as they underwent Friedel-Crafts reaction with the aldehyde. Toluene gave a mixture of ortho- and para-substituted products in a 2:1 ratio.