A series of bicyclic anhydro-4-hydroxy-2-oxo-1,3-thiazinium hydroxides containing tethered Ï-systems are easily prepared from the reaction of thiolactams with 1,3-bielectrophiles. These cross-conjugated heteroaromatic betaines undergo regio- and stereospecific 1,4-dipolar cycloaddition in good yield to produce cycloadducts containing a carbonyl sulfide bridge which can be induced to lose COS on further heating. Two of the cycloadducts were characterized by single crystal X-ray determinations. Control of ring size in the final product of the cycloaddition can be achieved by variation of the dipolarophilic chain length. Entry to the [6,6,5]- and [6,6,6]pyridone ring systems was possible using phenylalkynyl-substituted thioamides. Intramolecular 1,4-dipolar cycloaddition of a thiazinium betaine dipole also occurs across an indolyl Ï-bond. With only one substituent group in the 9-position of the bicyclic betaine, the reaction takes an entirely different course unless a highly activated Ï-bond is incorporated into the tether. The preferred reaction with modestly activated Ï-systems corresponds to loss of the activated proton to produce an S,N-ketene acetal. When a ketene S,S-acetal group was incorporated onto the side chain, the 1,4-dipolar cycloaddition reaction was facilitated relative to proton loss.
一系列含有联接π系统的双环无
水-
4-羟基-2-
氧-1,3-
噻唑鎓
氢氧化物可以通过
硫内
酰胺与
1,3-双电亲体的反应轻松制备。这些交错共轭的杂芳香族贝塔因在良好的产率下经历区域性和立体特异性的1,4-偶极环加成,生成含有
羰基硫桥的环加成物,在进一步加热时可以诱导失去C
OS。通过单晶X射线测定对其中两个环加成物进行了表征。通过改变偶极亲核链的长度,可以控制环加成反应最终产物的环大小。使用
苯基炔基取代的
硫氨基可以实现对[6,6,5]-和[6,6,6]
吡啶酮环系的导入。
噻唑鎓贝塔因偶极的环内1,4-偶极环加成也发生在
吲哚的π键上。在双环贝塔因的9位仅有一个取代基时,反应的路径会完全不同,除非在连结中加入一个高度活化的π键。与适度活化的π系统的优选反应对应于活化质子的失去,从而生成S,N-
烯酮缩醛。当在侧链上引入
烯酮S,S-
缩醛基时,相较于质子失去,1,4-偶极环加成反
应得以促进。