Synthesis of the Common Monomeric Unit of Uroleuconaphins and Viridaphins via Hauser–Kraus Annulation

Abstract

A stereoselective synthesis of a pyranonaphthoquinone derivative found in aromatic polyketide-derived aphid pigments is reported herein. This approach features the anionic [4+2]-annulation of phthalides with a carbohydrate-derived optically active enone. Additional synthetic steps provide access to the monomer fragment of uroleuconaphins and viridaphins. The optimization for a facile preparation of phthalides bearing sulfonyl or cyano groups are also studied.

Synthesis of Natural Products, Carbocycles, and Heterocycles by Hauser–Kraus Annulation

“…Scheme 10 Synthesis of dihydro-isocoumarins and furomollugin core Very recently, Kaku and co-workers described the synthesis of a common monomeric unit of naturally occurring uroleuconaphins and viridaphins through H-K annulation (Scheme 11). 28 The Kraus annulation of 3-cyanophthalide 89 with enone 90 furnished the product 91 in 96% yield, while the Hauser annulation of sulfonylphthalide furnished 91 only in 78% yield. The reduction of carbonyl in the presence of NaBH4 followed by oxidation of hydroxyl groups mediated by ceric ammonium nitrate delivered the natural product inspired target molecule 92 in excellent yield (98%, two steps).…”

Silica gel-mediated chemical degradation of dimeric pyranonaphthoquinones into their monomeric units

“…The treatment of 5b with silica gel (pH 7) in MeOH (0.002 M) at 80 °C promoted the degradation of the dimeric structure to provide its monomeric pyranonaphthoquinones 6 (21%), 7 (21%), and 8 (28%). 11 The reaction did not proceed in common organic solvents, such as toluene, chlorobenzene, or ethyl acetate. In contrast, the reaction using 5a , the C(10a)–α–H diastereomer, was sluggish to complete the degradation for five days because of the significantly slower enolization at C10a.…”