A facile synthesis of fused spiroketal skeleton: 2,2′-spirobi(4-aryl-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydrochroman)

A one-pot synthesis of fused spiroketal skeleton, 2,2′-spirobi(4-aryl-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydrochroman) 4a–c, has been achieved for the first time by an application of Michael reaction between dimedone (5,5-dimethylcyclohexan-1,3-dione) 1 and trans,trans-diarylideneacetone (1,5-diaryl-1,4-pentadien-3-one) 2 using anhydrous ZnCl2 as catalyst. The spiroketalization was achieved efficiently via intramolecular cyclization of the Michael 1:2 adduct.