Addition of HCl accelerated the photocyclodimerization of trans-4-styrylpyridine 1a in methanol and increased the yield of syn-head-to-tail (syn-HT) dimer 2a through the effect of cation-π interactions between the pyridinium ion of one molecule and the phenyl group of the other. We examined the photoirradiation products of derivatives of 1a having alkyl substituents on the phenyl group (1b–1f). The effect of the alkyl substituent on product distribution was rather limited for the photoreaction in MeOH solutions. However, the substituents had a distinct effect on the product distribution for the photoreaction of the inclusion complexes of hydrochloride salts of trans-4-styrylpyridines with cucurbit[8]uril in aqueous solutions. Introducing an alkyl group at the 2- or 3-position of the phenyl group completely shifted the major product from the syn-HT dimer to the syn-head-to-head (syn-HH) dimer. By adjusting the balance of host–guest interactions and cation-p interactions between guest molecules through systematic changes in the substituents on the phenyl ring of trans-4-styrylpyridine, we could change the orientation of the reactant molecules in the host cavity, resulting in a change of the major regioisomer of the photocyclodimerization products.
通过一个分子中的
吡啶离子与另一个分子中的苯基之间的阳离子-π相互作用的影响,加入
盐酸加速了反式-4-
苯乙烯吡啶 1a 在
甲醇中的光环二聚化,并增加了合成头尾(syn-HT)二聚体 2a 的产率。我们研究了苯基上有烷基取代基的 1a 衍
生物(1b-1f)的光辐射产物。在 MeOH 溶液中进行光反应时,烷基取代基对产物分布的影响相当有限。但是,对于反式-4-
苯乙烯吡啶盐酸盐与葫芦[8]
脲的包合物在
水溶液中的光反应,取代基对产物分布有明显的影响。在苯基的 2- 位或 3- 位引入一个烷基,会使主要产物从 syn-HT 二聚体完全转变为 syn-head-to-head (syn-HH) 二聚体。通过系统地改变反式-4-
苯乙烯吡啶苯环上的取代基,调整客体分子之间的主-客体相互作用和阳离子-阳离子相互作用的平衡,我们可以改变反应物分子在主腔中的取向,从而改变光环二聚产物的主要区域异构体。