3-Hydroxy-3-methyl-1,1-dimethoxybutane, a new reagent for dimethylchromenylation: synthesis of lonchocarpin, jacareubin, evodionol methyl ether, and other chromens

Like citral, 3-methylbut-2-enal condenses under pyridine catalysis with suitable meta-dihydric phenols to give chromens having the 2,2-dimethyl-substitution pattern common in Nature. Citral acetal and 3-methyl-1,1-dimethoxybut-2-ene can replace the free aldehydes, and this observation has led to the development of 3-hydroxy-3-methyl-1,1-dimethoxybutane as a stable and readily accessible dimethylchromenylation reagent. Synthesis of various dimethylchromens, among them lonchocarpin, jacareubin, and evodionol methyl ether, illustrate its use. But-2-enal and cinnamaldehyde may be used in chromenylation reactions.