This article surveys the various applications of ultrasound to organic synthesis and the fundamental aspects of sonochemistry. Sonochemical reactions in homogeneous and heterogeneous systems are discussed in connection with the cavitation phenomena. Particular attention is given to the activation of metal surfaces in organometallic chemistry. Sonochemical switching, sonocatalysis and sonochemical reactors are also discussed.
Recent Studies on regio- and stereoselective synthesis using transmetallation reaction of organotin compounds were reviewed. Regioselective 1, 4-dianion formations and its rearrangements, [2, 3] -sigmatropic rearrangements of allylic lithiomethyl ether and its applications to the chiral transfer reaction of steroidal side-chain, and transmetallaion of α-alkoxystannyl compounds with retention of configuration were discussed. Some applications to the total synthesis of natural products were also described.
Chemistry of thio-and selenoaldehydes has been reviewed focusing on advances in 1980's. The methods for the formation of thio-and selenoaldehydes are roughly divided into five types : (1) Norrish type II photoreaction of α-ketosulfides, (2) 1, 5-sigmatropic reactions of thiosulfinates and thioseleninates, (3) 1, 2-eliminations, (4) retro-Diels-Alder reactions of cycloadducts, and (5) reaction of organometallics with calcogenoformates. Thioaldehydes as reactive intermediates are generated mainly by methods (1) - (4), while stable thioaldehydes are synthesized by method (5) or thermolysis of polymer (RCHS) n. Any stable selenoaldehyde is yet unknown, but those as reactive intermediates can be formed by methods (3) - (5). Although a variety of reactions of thioaldehydes have ben studied using both reactive and stable species, those of selenoaldehydes have been so far limited almost exclusively to cycloadditions. Synthesis and reactions of metal complexes of thio- and selenoaldehydes are also briefly reviewed.
Diethyl phosphorocyanidate (DEPC) has been extensively utilized as a versatile reagent for cyanation under mild and non-aqueous reaction conditions. This article describes a new method for the synthesis of cyanophosphates by reaction of DEPC with various kinds of carbonyl compounds in the presence of lithium cyanide, and its application in organic synthesis is devided into four items : 1) synthesis of α, β-unsaturated nitriles and arylacetonitriles from aryl ketones via cyanophosphates, 2) synthesis of 3-aryl-4-hydroxybenzonitriles from p-benzoquinone cyanophosphates with aromatic and heteroaromatic compounds, 3) boron trifluoride etherate catalyzed allylic rearrangement of enone cyanophosphates and its application to β-cyanoenones, 4) 2-cyanoindole-3-acetonitriles from 3-indolecarbaldehydes via cyanophosphates and its application to carbazole derivatives by cycloaddition with activated alkynes.
Reductive elimination from square planar d8-organotranstion metal complexes of nickel (II), palladium (II) and gold (III) involving carbon-carbon bond formation has been considered as one of the most important fundamental steps in relation to various organic and catalytic reactions promoted by transition metal complexes. The mechanism for the reductive elimination varies depending on the metals, supporting ligands, oxidation states, structure of intermediate and etc. The stability of the intermediates are in the order of 3, 5 and 4-coordinate complexes. Carbon-carbon bond formation on the gold (III) is regio and stereo selective. Selectivity in the leaving organic group directly bonded to metals, strongly depends not only on the electronic factor, but also on the pπ charcter of the α-carbon.
Bis (perfluoroalkanoyl) peroxides were found to be useful reagents for perfluoroalkylations ; various perfluoroalkyl groups, such as perfluoromethyl, perfluoropropyl, or perfluoroheptyl, can be introduced into electron-rich benzenes, olefins, or heteroaromatic compounds in a similar procedure. The perfluoroalkylations proceed under mild conditions in high yields and regioselectively