A concise total synthesis of (±)-anthecularin

Abstract

A total synthesis of the novel sesquiterpene anthecularin 1, isolated from Greek Anthemis auriculata, based on an intramolecular [5+2] (1,3-dipolar) cycloaddition involving the oxidopyrylium ion 12 derived from the furanmethanol 9, is described.

Molecular Selective Binding and Nanofabrication of Cucurbituril/Cyclodextrin Pairs

“…Table 1 lists the binding constants of some representative dyes with cucurbiturils and cyclodextrins in aqueous solution. [21][22][23][24] As seen in Table 1, CB [7] forms moderately stable complexes with positively charged guests in buffer solution, showing a K S order of 2 > 1 > 3 in pH 6.0 buffer solution. A reasonable explanation for the highest binding ability of CB [7] towards 2 is that CB [7] can effectively bind the positive-charge portion of 1 or 3 mainly through ion-dipole interactions, while for 2, the hydrogen bond interactions between the middle NH group in 2 and C=O group in CB [7] possibly also play a crucial role in the host-guest complexation besides the ion-dipole interactions.…”

“…However, because of the intense charge repulsion between the carboxylate group of guest 8 À and the carbonyl oxygens on the CB [7] portals, the negatively charged guest 8 À is not bound at all by CB [7], although all of these ferrocene-containing guests can form stable inclusion complexes with b-CD regardless of their charge. [22][23][24] From the results described above, one can conclude that CB [7] is a better host for cationic guests than b-CD, especially in pure water. It should be noted that the addi-tion of salt greatly affects the binding abilities of cucurbiturils in aqueous solution.…”

“…Therefore, the binding strength of cationic guests with cucurbiturils can be effectively modulated by the adjustment of the salt concentration and the type of salt. [22,25]…”

Stereoselective Mannich Reaction of N‐(tert‐Butylsulfinyl)imines with 3‐Fluorooxindoles and Fluoroacetamides

“…We have an ongoing interest in the use of simple α‐carbonyl compounds to synthesize stereogenic C−F centers . Very recently, we showed that weakly acidic α‐fluoro carboxylate esters are competent fluorocarbon reagents that can be converted to α‐fluoro‐β‐amino acid derivatives through a highly diastereoselective Mannich reaction . Herein, we disclose an efficient Mannich reaction between 3‐fluorooxindoles and Ellman's imines to provide access to a wide variety of β‐amino amides containing α‐fluorinated stereogenic carbon centers (Scheme ).…”

Recent Developments in the [5+2] Cycloaddition

“…In 2009, Pattenden et al reported a concise total synthesis of the sesquiterpene anthecularin, a natural product exhibiting anti-malarial activity. [65] This synthesis was based on the intramolecular [5 + 2] cycloaddition of the acetoxypyranone-substituted butenolide 93. Indeed, when a solution of 93 in toluene containing DBU was heated under reflux for 1 h, the cycloaddition involving the corresponding oxidopyrylium species took place, leading to the tetracyclic product 92, albeit in low yield (15-20%), as illustrated in Scheme 40.…”