Organocatalytic Asymmetric Synthesis of Benzothiazolopyrimidines via [4 + 2] Cyclization of 2-Benzothiazolimines and Aldehydes.

We report the direct asymmetric synthesis of pyrimido[2,1-b]benzothiazoles using a commercially available chiral amine catalyst. A variety of 2-benzothiazolimines and aldehydes were well tolerated under the reaction conditions and generated the corresponding products in 81-99% yields with excellent diastereoselectivities and enantioselectivities (up to >20:1 dr, 99% ee). Furthermore, the products could be easily converted to other useful chiral building blocks.