An Organocatalytic Approach to Naphthoquinone Derivatives

Significance

An addition-cyclization reaction of hydroxynaphthoquinone 1 with various α,β-unsaturated aldehydes 2 is reported using diarylprolinol silyl ether 3 as catalyst. The corresponding products 4 were obtained with high enantioselectivity. According to the authors’ proposal the reaction proceeds via an iminium ion intermediate 5. A 1,4-addition of ketone 1 to iminium ion 5, followed by isomerization and subsequent hydrolytic acetylization leads to the desired product. The utility of products 4 was demonstrated by their conversion to β-lapachone derivatives 6 and corresponding lactones 7 without loss of enantiopurity.