Enantioselective Total Synthesis and Structure Confirmation of the Natural Dimeric Tetrahydroxanthenone Dicerandrol C

Abstract

The first enantioselective total synthesis of natural dicerandrol 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.

Scope and Limitations of the Domino Vinylogous Aldol/oxa‐Michael Reaction

“…by taking advantage of a vinylogous addition of siloxyfuranes to activated benzopyrylium salts and in a previous publication by our group: We employed a domino vinylogous aldol/ oxa ‐Michael reaction as the key step. The different approaches to tetrahydroxanthones culminated in the asymmetric syntheses of diversonol, −, lachnones, blennolides, , , , , , , secalonic acids and dicerandrol …”

Enantioselective Total Synthesis of Blennolide H and Phomopsis‐H76 A and Determination of Their Structure

“…[7,8] Treatmento f9 with Et 3 N·3 HF at 60 8Cf or four days gave the lactone 10 a in 83 %y ield. [7,8] Treatmento f9 with Et 3 N·3 HF at 60 8Cf or four days gave the lactone 10 a in 83 %y ield.…”

“…[7,8] Treatmento f9 with Et 3 N·3 HF at 60 8Cf or four days gave the lactone 10 a in 83 %y ield. [8] In order to allow the dimerization, compound 11 a was protecteda samethoxymethyl ether (MOM) prior to the Suzukir eaction using MOMCl to give 12 in 95 %y ield. [23] The orthoiodide 11 a was then subjected to Suzukic onditions using Pd(OAc) 2 ,S Phos, B 2 pin 2 ,a nd K 3 PO 4 but under these conditions only decomposition of 11 a was observed, probablyd ue to the free hydroxymethyl group in connection with the lactone moiety,a sd imerization of monomeric compounds with free phenolic hydroxy groups and hydroxymethyl groupsh ave been previously accomplished.…”

“…We therefore compared the published NMR data of the dimeric 6 with the available information of different monomeric chromanone lactones. [7,8] Treatment of 14 with BnNMe 3 ICl 2 gave the desired orthoiodide 15 a as the main product in 50 %y ield;i na ddition, the para-iodide 15 b and the diiodide 15 c were formed,both in 6% yield. [25] By comparing all NMR data, the best correlation with the dimer was found form onomer 14, [24] which was then used as starting materialf or the synthesis of blennolide H (6)( Scheme2).…”

“…synthesized,f or the first time, secalonic acid D( 1)a nd Ab ym eanso faStille type dimerization in good yields, [6] and one year later Tietze et al described the first enantioselective synthesis of secalonic acid E( 2)b ym eanso faSuzuki type dimerization again in good yield and with 99 %e nantioselectivity. [8] Besides the 2,2'-biphenyl axis, compounds with a4 ,4'-axis such as phomoxanthone A( 4)a s well as several heterodimers are also known. Last year ad icerandrol, namely dicerandrol C( 3c), was prepared by the Tietze group as its enantiomer in an enantioselective way using aW acker oxidation for the first time.…”