LAUSR

Chiral heterocycles are widely occurring in many compounds of interest, but their efficient synthesis is challenging. We present here the enantioselective and diastereoselective synthesis of densely substituted chiral pyran derivatives. Diastereodivergency of the oxa-Diels-Alder reaction was achieved using either bifunctional amino-thiourea or monofunctional quinine organocatalyst under ball-milling conditions. Liquid-assisted grinding was highly efficient for affording pyrans in high yields, high enantiomeric purities, and short reaction times.