Studies in the synthesis of 1,2-dithiins and 1,2-diselenins.

摘要

The evolution of a strategy culminating in an efficient formal synthesis of thiarubrine A is described. Highlights of this synthesis are a stepwise method to synthesize the unsymmetrically substituted (Z,Z)-1,3-butadiene, the three-fold use of Sonogashira coupling reactions for the introduction of two different side chains and the formation of the carbon-carbon bond between C-4 and C-5, as well as the employment of the 2-(trimethylsilyl)ethyl sulfur protecting group. In this part of the study, some novel reactions are also presented, including (1) a new, reliable protocol for the multigram scale preparation of sulfenamides as electrophilic sulfur-transfer reagents, (2) the novel application of these reagents in the synthesis of alkynylsulfides with removable sulfur protecting groups, (3) the regio- and stereoselective synthesis of three tri-functionality substituted alkenes for the first time under the heterogeneous conditions developed in this study.; A series of novel bicyclic-1,2-dithiins and their selenium analogues, namely [d]-annulated 1,2-dichalcogenins is synthesized via a three-step sequence in one pot from common precursors: halogen-metal exchange with n-butyllithium in diethyl ether at -78 °C, treatment with elemental sulfur or selenium, and oxidation with oxygen. Photochemistry of these annulated 1,2-dichalcogenins is studied. Geometrical changes of the 1,2-dithiin ring caused by the 4-membered ring [d]-annulation, their bathochromically shifted UV-vis absorption maxima, as well as the remarkable stability of these [d]-annulated 1,2-dithiins toward visible light are also discussed.; A flexible synthetic approach to the core structure of 1,2-dithiabicyclo[4.2.0]octa-3,5,7-triene is proposed and attempted. In the first part of this study, an efficient and concise synthesis of three novel functionalized bis(methylene)cyclobutene derivatives with the requisite Z,Z configuration of the double bonds is presented. The double bond in the 4-membered ring is introduced through deoxygenation reactions either from thionocarbonate precursors via Corey-Winter reaction or from dimethylamino-dioxolane precursors following Yang's methodology. In the second part, a functionalized tricyclic 1,2-dithiin is prepared via a relatively longer route due to the necessity of the protection and deprotection of the diol moiety present in the molecule. During the course of this study, a facilitating effect of the 1,3-dioxolane annulated ring on the ring closure of 1,5-diynes was discovered. The development of a novel and convenient protocol for the preparation of 1,6-diphenylhexa-1,5-diyne-3,4-dione is also described.