Current Organic Chemistry - Volume 24, Issue 12, 2020

Replacing harmful organic solvents that caused environmental pollution with an alternative medium for the development of ideal synthetic strategies is one of the primary focal points of green chemistry. Utilizing polyethylene glycol (PEG) as a nonvolatile solvent and promotor for the evaluation of safe processes has made a considerable contribution to the reduction of pollution problems. The current review summarizes the recent well-known catalyst-free organic reaction performed in polyethylene glycol as a green and biocompatible reaction medium.

Gorgonian corals are considered as a rich source of secondary metabolites with unique structural features and biological activities. A large number of novel metabolites with potent pharmacological properties have been isolated from gorgonian corals. Some of these compounds have exhibited to possess new mechanisms of action, which hold great promises as potential lead compounds in future marine drug development. This review aims to provide an overview of chemical constituents and biological activities of gorgonian corals from 2015 to December, 2019. Some 145 metabolites, including 16 sesquiterpenoids, 62 diterpenoids, 62 steroids and 5 alkaloids were reported during this period and their pharmacological activities were investigated. Moreover, the peculiar structure and potential medicinal value of these new compounds are discussed in this review.

The effective and high yielding synthesis of poly-functionalized pyrimidines, using multicomponent reactions (MCRs), is imperative in organic and medicinal chemistry. The classic Biginelli reaction is a typically one-pot three-component cyclocondensation reaction involving an aldehyde, a β-ketoester and urea, resulting in the construction of multi-functionalized 3,4-dihydropyrimidin-2(1H)-ones (DHPMs). In recent years, other active methylene compounds, various derivatives of urea and diversely substituted aldehydes have also been used, resulting in the preparation of a new series of various novel dihydropyrimidinones via the Biginelli-Type Reactions (BTRs) or modified Biginelli reactions (MBRs). In this review, we try to underscore the recent advances in BTRs or MBRs.

The mechanism studies of transition-metal-catalyzed reductive coupling reactions investigated using Density Functional Theory calculations in the recent ten years have been reviewed. This review introduces the computational mechanism studies of Ni-, Pd-, Cu- and some other metals (Rh, Ti and Zr)-catalyzed reductive coupling reactions and presents the methodology used in these computational mechanism studies. The mechanisms of the transition- metal-catalyzed reductive coupling reactions normally include three main steps: oxidative addition; transmetalation; and reductive elimination or four main steps: the first oxidative addition; reduction; the second oxidative addition; and reductive elimination. The ratelimiting step is most likely the final reductive elimination step in the whole mechanism. Currently, the B3LYP method used in DFT calculations is the most popular choice in the structural geometry optimizations and the M06 method is often used to carry out single-point calculations to refine the energy values. We hope that this review will stimulate more and more experimental and computational combinations and the computational chemistry will significantly contribute to the development of future organic synthesis reactions.

An efficient decarboxylative cycloaddition of 2,3-dioxopyrrolidines and ethynyl benzoxazinanones has been established by cooperative copper/amine catalysis. A copper– allenylidene complex and enolate intermediate, each catalytically generated from distinct substrates, underwent a cascade propargylation/hydroamination/aromatization process to construct a big library of cyclopenta[b]indole derivatives with good to excellent yields and excellent diastereoselectivity.