The Diels-Alder reaction, one of the most popular [4+2] cycloaddition reactions, is the best way to construct the six-membered ring compounds. This review deals with the recent (mainly after 1980) advance in the reactions utilizing a variety of novel diene systems with 196 references.
Two successful syntheses of cytochalasins accomplished at Columbia University are described in a context of general problems associated with the synthesis of this class of compounds. The key features of the syntheses involve a regio- and stereoselective Diels-Alder reaction of an enol lactam, e. g., 57, and a triene, e. g., 49, followed by stereocontrolled formation of 6, 7-epoxide (to cytochalasin F, 3), which is then transformed to Δ6 (12) -allylic alcohol (to cytochalasin B, 2). The first synthesis solved these fundamental structural problems and the second streamlined the overall strategy by using a macrocyclic internal Diels-Alder reaction and some new phosphorus and aluminium reagents.
Lignans and neolignans are plant products formed by the oxidative dimerization of various C6-C3 phenols. Since lignans and neolignans have varied types of structures and show broad range of biological activities, they have received a great deal of synthetic attention, and many elegant syntheses have been reported. This review deals with recent progress in the total synthesis of lignans and neolignans. Particular emphasis has been placed on biomimetic synthesis by using anodic oxidation of phenols.
The ionophorous antibiotics are a member of compounds possessing the ability to form complex with alkali ions and to carry ions across lipid barrier including artificial and biological membranes. These antibiotics have been employed as tools for studying properties of membrane-bound carriers as well as the molecular basis of biological ion discrimination. This report described the property of cation ionophores and some of biological applications of these substances.
Recent studies on organic photochemical reactions induced by UV, visible, and IR lasers are briefly reviewed with regard to applications of laser chemistry to organic syntheses. This review describes (1) laser photochemical reactions from the synthetic point of view, (2) single- and multiple-photon processes induced by UV and visible lasers, (3) IR multiple-photon decomposition and selective IR photochemical reactions of organic compounds induced by CO2 lasers, (4) laser photochemical reactions in solids and on surfaces of solids, and (5) laser photochemical reactions of organometallic compounds.
Research and development on the preparation of novel polymer microspheres and their applications have been accelerated in this decade. This article deals with polymer catalysts and reagents which have functional groups on and in polymer microspheres or beads. Immobilization of functional groups on polymer microspheres causes not only simplification of the recovery of reagent from the reaction system, but also changes in the rate, selectivity, and pattern of reaction in most cases. Dependence of these changes on the physical and chemical structure of polymer microspheres is discussed and a guide is given for the preparation of polymer microspheres having desirable functions.
Besides MTG (methanol to gasoline) process, synthesis of lower olefins such as ethylene and propene received much attention. Recent development in synthesis of lower olefins by methanol conversion over zeolite and non-zeolite catalysts has been described. Reaction pathway and reaction mechanism are briefly mentioned. The modification of ZSM-5 with trimethyl phosphite, etc., enhanced the selectivity. Small-pore zeolites such as erionite and ZSM-34 produce only low molecular weight hydrocarbons, which is due to the shape-selectivity. A serious problem of these zeolites is their short-life time owing to rapid deactivation through coke formation. In heteropoly compounds, the olefin-selectivity is improved as the contribution of the bulk phase of catalysts (pseudo-liquid phase) decreases.