Aliphatic Thiocarbonyl Ylides and Thiobenzophenone: Experimental Study of Regiochemistry and Methylene Transfer in Cycloadditions
Aliphatic Thiocarbonyl Ylides and Thiobenzophenone: Experimental Study of Regiochemistry and Methylene Transfer in Cycloadditions
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脂肪族硫代羰基叶立德和硫代二苯甲酮：环加成反应中区域化学和亚甲基转移的实验研究
DOI：
10.1002/ejoc.200400765
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发表时间：
2005
影响因子：
2.8
通讯作者：
R. Sustmann
中科院分区：
文献类型：
--
作者：
R. Huisgen;G. Mlostoń;H. Giera;E. Langhals;K. Polborn;R. Sustmann
脂肪族或脂环型硫代羰基叶立德3A-D与硫代二苯甲酮的1，3-偶极环加成反应均产生区域异构体1，3-二硫杂环戊烷4和5。根据量子化学计算(前文)，2，4-取代二硫杂环戊烷4的协同环加成反应与中间体C，C-双自由基9的形成竞争，后者环化到更密集的4，5-取代二硫杂环戊烷5上。当3的空间位阻增加时，环加成反应被‘亚甲基转移’所取代，即3E-J的末端受阻较小的转移到硫代苯甲酮的S原子上。由此形成的硫代二苯甲酮S-烷基醚11通过高度稳定的C，C-双自由基10与第二个硫代二苯甲酮快速反应生成4，4，5，5-四苯基-1，3-二硫杂环戊烷12。当混合的C，C-双自由基9的环化反应需要比其解离为脂肪族硫酮+11更高的活化势时，发生亚甲基转移，计算结果令人惊讶地重现了这个阈值。16个1，3-二硫杂环戊烷的结构归属是基于它们由相应的反应物对以及1H和13C化学位移形成的。三个螺环-1，3-二硫杂环戊烷的X射线衍射分析表明，在非键相互作用、折叠角、剪切力和键长中存在范德华应变。通过比较许多1，3-二硫杂环戊烷的质谱图，可以重建主要的裂解途径。(Wiley-VCH Verlag GmbH&Co.KGaA，69451，德国温海姆，2005年)
1,3-Dipolar cycloadditions of aliphatic or alicyclic thiocarbonyl ylides 3A-D – sterically hindered at least at one terminus – with thiobenzophenone produce both regioisomeric 1,3-dithiolanes 4 and 5. According to quantum-chemical calculations (preceding paper), a concerted cycloaddition furnishing 2,4-substituted dithiolanes 4 competes with the formation of an intermediate C,C-biradical 9 which cyclizes to the more crowded 4,5-substituted dithiolanes 5. When steric hindrance of 3 increases, the cycloaddition is superseded by ‘methylene transfer’, i.e., the transfer of the less hindered terminus of 3E-J to the S-atom of thiobenzophenone. The thiobenzophenone S-alkylide 11, thus formed, rapidly reacts with a second molecule ofthiobenzophenone to generate the 4,4,5,5-tetraphenyl-1,3-dithiolane 12 via the highly stabilized C,C-biradical 10. Methylene transfer occurs when the cyclization of the mixed C,C-biradical 9 requires a higher activation barrier than its dissociation to aliphatic thioketone + 11; the threshold is surprisingly well reproduced by calculations. The structural assignment of sixteen 1,3-dithiolanes is based on their formation from corresponding reactant pairs as well as on 1H and 13C chemical shifts. X-ray diffraction analyses of three spiro-1,3-dithiolanes reveal the van der Waals strain in non-bonded interactions, folding angles, shearing forces, and bond lengths. Comparison of the mass spectra of many 1,3-dithiolanes allows the reconstruction of major fragmentation pathways. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)