Research Group for Carbohydrates, University of Debrecen, PO Box 94, H-4010 Debrecen, Hungary.
Org Biomol Chem. 2013 Aug 28;11(32):5339-50. doi: 10.1039/c3ob40547h.
Exo- and endocyclic double bonds of glycals and terminal double bonds of enoses were reacted with various thiols by irradiation with UV light in the presence of a cleavable photoinitiator. The photoinduced radical-mediated hydrothiolation reactions showed highly varying overall conversions depending not only on the substitution pattern and electron-density of the double bond but also on the nature and substitution pattern of the thiol partner. Out of the applied thiols thiophenol, producing the highly stabilized thiyl radical, exhibited the lowest reactivity toward each type of alkene. In most cases, the hydrothiolations took place with full regio- and stereoselectivities. Successful addition of 1,2 : 3,4-di-O-isopropylidene-6-thio-α-d-galactopyranose to a 2,3-unsaturated N-acetylneuraminic acid derivative, providing a (3 → 6)-S-linked pseudodisaccharide, demonstrated that the endocyclic double bond of Neu5Ac-2-ene, bearing an electron-withdrawing substituent, shows sufficient reactivity in the photoinduced thiol-ene coupling reaction.
糖醛和烯糖的内外环双键以及末端双键与各种硫醇在可裂解光引发剂的存在下通过紫外线照射反应。光诱导自由基介导的氢硫加成反应显示出高度变化的总转化率，不仅取决于双键的取代模式和电子密度，还取决于硫醇配体的性质和取代模式。在所应用的硫醇中，产生高度稳定的硫自由基的苯硫酚对每种类型的烯烃表现出最低的反应性。在大多数情况下，氢硫加成反应具有完全的区域和立体选择性。成功地将 1,2:3,4-二-O-亚异丙基-6-硫-α-D-半乳糖吡喃糖添加到 2,3-不饱和 N-乙酰神经氨酸衍生物中，提供了一个(3→6)-S 连接的假二糖，证明了带有吸电子取代基的 Neu5Ac-2-烯的内环双键在光诱导的硫醇-烯偶联反应中具有足够的反应性。
