Enantioselective Total Synthesis of Secalonic Acid E

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 18 steps with 8 % overall yield.     

Insertion reactions of macrocyclic rhodium carbenoids: a novel method for the synthesis of cryptands

Reaction of macrocyclic diazocarbonyl compounds and alcohols or diols in the presence of rhodium(II) acetate catalyst led to functionalized macrocyclic di- or tetralactones via O-H insertion. Interestingly, the double O-H insertion reaction with dihydroxy compounds gave cryptands of various ring sizes.     

Ionic liquids as a convenient recyclable medium for the generation of transient carbonyl ylides: syntheses of oxa and dioxa-bridged polycyclic systems

The tandem cyclization-cycloaddition reactions of α-diazo ketones in the presence of rhodium(II) acetate, rhodium(II) octanoate or copper(II) acetyl acetonate as catalyst were performed in different imidazole based ionic liquids as solvent. A successful generation of the transient five- or six-membered-ring carbonyl ylides, followed by the 1,3-dipolar cycloaddition with olefin or carbonyl functional groups in ionic liquid is described to furnish the oxa and dioxa-bridged polycyclic systems with high stereoselectivity. Significant advantages of this process are the recovery of rhodium catalyst, the re-use of ionic liquid, replacement of hazardous organic solvents and the resulting high stereoselectivity.     

Recent Advances in the Metal‐Catalyzed Activation of Amide Bonds

The amide functional group is commonly found in peptides, proteins, pharmaceutical compounds, natural products, and polymers. The synthesis of amides is typically performed by using classical approaches that involve the reaction between a carboxylic acid and an amine in the presence of an activator. Amides are thought to be an inert functional group, because they are unsusceptible to nucleophile attack, owing to their low electrophilicity. The reason for this resistance is clear: the resonance stability of the amide bond. However, transition metal catalysis can circumvent this stability by selectively rupturing the N?C bond of the amide, thereby facilitating further cross‐coupling or other reactions. In this Focus Review, we discuss the recent advances in this area and present a summary of methods that have been developed for activating the amide N?C bond by using precious and non‐precious metals.     

A direct method to visualise the aryl acylamidase activity on cholinesterases in polyacrylamide gels

Background  

In vertebrates, two types of cholinesterases exist, acetylcholinesterase and butyrylcholinesterase. The function of acetylcholinesterase is to hydrolyse acetylcholine, thereby terminating the neurotransmission at cholinergic synapse, while the precise physiological function of butyrylcholinesterase has not been identified. The presence of cholinesterases in tissues that are not cholinergically innervated indicate that cholinesterases may have functions unrelated to neurotransmission. Furthermore, cholinesterases display a genuine aryl acylamidase activity apart from their predominant acylcholine hydrolase activity. The physiological significance of this aryl acylamidase activity is also not known. The study on the aryl acylamidase has been, in part hampered by the lack of a specific method to visualise this activity. We have developed a method to visualise the aryl acylamidase activity on cholinesterase in polyacrylamide gels.