(Pyridinylmethylidene)dithioles: synthesis, structure, and reactivity
摘要:
Spectral characteristics, an X-ray crystal structure, and molecular orbital calculations indicate that (pyridinylmethylidene)dithioles 3, prepared from butadiynyl precursors 4 and hydrogen sulfide in basic methanol, are analogous in their bonding to the parent 1-aza-6,6a-lambda-4-dithiapentalenes 1 which, according to ab initio studies at the Hartree-Fock level, is best represented as an (iminomethylidene)dithiole. An interaction between the sulfur and the nitrogen atoms is evident from the significant polarization of the S-S bond in those isomers where the nitrogen is proximal to the dithiole moiety. A comparison of the calculated structures of 1 and 3 with experimental data, as well as preliminary calculations on the related system trithiapentalene 2, suggest that ab initio methods using a single determinant are inadequate to describe these hypervalent sulfur systems. For example, an asymmetric structure is calculated to be the minimum energy form for 2 in contradiction to experimental results. Electrophilic substitutions, ring rearrangement, and reaction with electron acceptors are described for 3.
A convenient route to 1,3-diynes using ligand-free Cadiot-Chodkiewicz coupling reaction at room temperature under aerobic conditions
作者:Sujatha Asha、Sasidharan Anjana、Anns Maria Thomas、Minu Elizabeth Thomas、K. R. Rohit、K. Keerthi Krishnan、Sankuviruthiyil M Ujwaldev、Gopinathan Anilkumar
DOI:10.1080/00397911.2018.1554142
日期:2019.1.17
Abstract In this study, we report a copper-catalyzed ligand-free Cadiot-Chodkiewicz couplingreaction. No additives or ligands are required for this Cu-catalyzed C(sp)-C(sp) couplingreaction of terminal alkynes with alkynyl halides. The low cost of copper catalyst, excellent yield of the products, suppression of side-products and mild reaction conditions are the major advantages of this protocol.
An iron-based catalytic system was developed for the cross-coupling of 1-bromoalkynes with terminalalkynes to selectively generate unsymmetrical 1,3-butadiynes in water under air. It was found that a combination of 1-bromoalkynes derived from less acidicterminalalkynes with more acidic counterparts would greatly enhance yields and selectivity for unsymmetrical 1,3-butadiynes. The reaction was also