ABSTRACT
The first enantioselective total synthesis of natural dicerandrolâ C (1 c) as its enantiomer containing a dimeric tetrahydroxanthenone skeleton is described starting from the enantiopure chromane 6 which was obtained through a Wacker-type cyclization with >99 % ee. For the formation of the dimeric skeleton a palladium-catalyzed Suzuki reaction was used. The synthesis allowed the confirmation of the absolute configuration of the dicerandrols.
Subject(s)
Xanthones/chemistry , Xanthones/chemical synthesis , Catalysis , Cyclization , Dimerization , Palladium/chemistry , Stereoisomerism , Xanthenes/chemistryABSTRACT
The first enantioselective synthesis of a secalonic acid containing a dimeric tetrahydroxanthenone skeleton is described, using a Wacker-type cyclization of a methoxyphenolic compound to form a chiral chroman with a quaternary carbon stereogenic center with >99% ee. Further steps are a Sharpless dihydroxylation and a Dieckmann condensation to give a tetrahydroxanthenone. A late-stage one-pot palladium-catalyzed Suzuki-dimerization reaction leads to the 2,2'-biphenol linkage to complete the enantioselective total synthesis of secalonic acid E in 18â steps with 8% overall yield.
ABSTRACT
Blennolideâ A can be synthesized through an enantioselective domino-Wacker/carbonylation/methoxylation reaction of 7a with 96 % ee and an enantioselective Wacker oxidation of 7b with 89 % ee. Further transformations led to the α,ß-unsaturated ester (E)-17, which was subjected to a highly selective Michael addition, introducing a methyl group to give 18a. After a threefold oxidation and an intramolecular acylation, the tetrahydroxanthenone 4 was obtained, which could be transformed into (-)-blennolideâ A (ent-1) in a few steps.
Subject(s)
Biological Products/chemical synthesis , Xanthones/chemical synthesis , Biological Products/chemistry , Catalysis , Fungi/chemistry , Fungi/metabolism , Oxidation-Reduction , Palladium/chemistry , Stereoisomerism , Xanthones/chemistryABSTRACT
For the synthesis of (-)-diversonol (ent-1), an enantioselective domino-Wacker/carbonylation/methoxylation reaction and an enantioselective Wacker oxidation were used to give the chroman in high yield and 96% and 93% ee, respectively. Dihydroxylation at the vinyl moiety using the Sharpless procedure and a Wittig-Horner reaction followed by hydrogenation, benzylic oxidation, and an intramolecular acylation provided the tetrahydroxanthenone, from which ent-1 is accessible in a few steps. Furthermore, the synthesis of the diastereomeric diversonol rac-1,9a-epi-diversonol (rac-41) is also described.
