Synthesis, Structure, and Bonding of 1-Oxa-6,6aλ4- chalcogenopentalenes and Related Derivatives; The Role of Intramolecular Coordination

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• 作者：Poonam Rajesh Prasad ; Karuthapandi Selvakumar ; Harkesh B. Singh ; Ray J. Butcher
• 刊名：Journal of Organic Chemistry
• 出版年：2016
• 出版时间：April 15, 2016
• 年：2016
• 卷：81
• 期：8
• 页码：3214-3226
• 全文大小：613K
• 年卷期：0
• ISSN：1520-6904

文摘

The synthesis and characterization of a series of alicyclic organochalcogen compounds derived from 2-chloro-1-formyl-3-hydroxymethylenecyclohexene (16) are described. The reaction of 16 with disodium disulfide afforded an unexpected 1-oxa-6,6aλ⁴-dithiapentalene 33, whereas the reaction of disodium diselenide afforded 1-oxa-6,6aλ⁴-diselenapentalene 34, along with 1,6-dioxa-6a-selenapentalene 35. In contrast, when 16 was treated with Na₂Te₂, it resulted in the formation of 1-oxa-6,6aλ⁴-ditellurapentalene 36 along with 1,6-dioxa-6a-tellurapentalene 37 and cyclic monotelluride 38. The oxidation of 1-oxa-6,6aλ⁴-diselenapentalene 34 with m-CPBA provided the corresponding 1-oxa-6,6aλ⁴-diselenapentalene-6,6aλ⁴-dioxide 39 in which both of the selenium atoms were found to be oxidized. The 1-oxa-6,6aλ⁴-dichalcogenopentalenes 33, 34, and 36 are stabilized by 3c-4e bond resulting from intramolecular E···O interaction. The donor oxygen donates a lone pair of electrons to the σ* orbital of acceptor E–E bond (E = S, Se, and Te) whose σ bond already has its bond pair electrons. The existence of intramolecular E···O interactions was established by multinuclear NMR spectroscopy, single crystal X-ray analysis, and computational studies. The single crystal X-ray structures of compounds 33, 34, and 36 reveal that the molecules are almost planar. Nucleus-independent chemical shifts were calculated to compare the aromaticity in both the five-membered rings of 33, 34, 36 and 1,6-dioxa-6a-chalcopentalenes (35 and 37). The isotropic shift values of the covalently fused five-membered heterocyclic rings are more negative than the five-membered heterocyclic rings formed by intramolecular coordination.