Starting from 3,5-dimethoxybenzaldehyde, some functionalized 2,3,4-trisubstituted tricyclic 4,5-cycloalkyl-fused and 6-modified chromans could be prepared via ortho-quinone methides (o-QMs)/hetero-Diels-Alder (HDA) reactions of the appropriate precursors. The bromide at C6 served as a handle for introducing other substituents through palladium-catalyzed cross-coupling reactions and other functional-group transformations. Moderate to high yields (up to 80%) and diastereoselectivities (up to >99:1) could be obtained under [PtCl4 ] catalysis. The preferred endo transition state during the cycloaddition reaction played an important role in governing the stereochemical outcomes at C2 - C3 - C4. The configurationally fixed E geometry of the bicyclic o-QMs influenced the cycloaddition reactions to favor the C2 - C4 cis relationship.
Synthesis of C4-C5 Cycloalkyl-Fused and C6-Modified Chromans via ortho--Quinone Methides. -The title chromans are synthesized via ortho-quinone methides/hetero-Diels-Alder reactions. It is found that the C-6 modifications by palladium-catalyzed Suzuki reactions affording 6-arylated chromans are more effectively performed at the aldehyde stage than at the chroman stage. -(TANGDENPAISAL, K.; CHUAYBOONSONG, K.; SUKJAREAN, P.; KATESAMPAO, V.; NOIPHROM, N.; RUCHIRAWAT, S.; PLOYPRADITH*, P.; Chem. -Asian J. 10 (2015) 4, 1050-1064, http://dx.
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