Enantioselective total synthesis of altersolanol A and N.

The development of the first enantioselective total synthesis of altersolanol N is reported. The decisive step of the synthesis is the enantioselective formation of the tetrahydroanthraquinone nucleus by a [4 + 2]-cycloaddition in high yield and with excellent diastereo- and enantioselectivity (>95:5 dr and 95:5 er). In addition, a demanding selective monoacetylation of the OH group at the C-2 position was achieved: an epoxide ring opening with the participation of a neighbouring acetyl group could be established. The route proved to be an efficient alternative to also access enantiomerically pure altersolanol A.

First enantioselective total synthesis of altersolanol A.

The first enantioselective total synthesis of altersolanol A, a secondary metabolite from the endophytic fungi Stemphylium globuliferum and Alternaria solani, is described. The key step towards the tetrahydroanthraquinone core was an asymmetric Diels-Alder (D-A) cycloaddition promoted by (R)-3,3'-diphenyl-BINOL/boron Lewis acid with good to excellent yields and excellent diastereo- and enantioselectivity (>95 : 5 dr and 98 : 2 er).