Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543.
J Org Chem. 2011 Oct 7;76(19):7860-5. doi: 10.1021/jo201268p. Epub 2011 Aug 29.
trans-3-(4'-Pyridyl)acrylic acid (4-PA) is inert to photodimerization reaction both in solution and solid state. It is made photoreactive by forming salts with various acids. The anions of these salts play a key role in directing the packing of 4-PAH(+) in the solid state. The anions CF(3)CO(2)(-), Cl(-), ClO(4)(-), and BF(4)(-) direct the parallel alignments of 4-PAH(+) in head-to-tail (HT) fashion and lead to the formation of HT-photodimer. On the other hand, bivalent anion SO(4)(2-) directs parallel alignment of 4-PAH(+) in head-to-head (HH) fashion and lead to the formation of HH-photodimer. The details of the anion-controlled stereoselective syntheses of these two cyclobutane derivatives are presented. Interestingly, both cyclobutane compounds undergo isomerization from rctt-form to rctc-form in solution catalyzed by acid.
反式-3-(4'-吡啶基)丙烯酸（4-PA）在溶液和固态中均对光二聚反应无反应活性。通过与各种酸形成盐，它变得具有光反应性。这些盐的阴离子在指导 4-PAH（+）在固态中的堆积方式方面起着关键作用。阴离子 CF3CO2（-）、Cl（-）、ClO4（-）和 BF4（-）指导 4-PAH（+）以头对头（HT）的方式平行排列，并导致 HT-光二聚体的形成。另一方面，二价阴离子 SO4（2-）指导 4-PAH（+）以头对头（HH）的方式平行排列，并导致 HH-光二聚体的形成。介绍了这些两种环丁烷衍生物的阴离子控制立体选择性合成的详细情况。有趣的是，这两种环丁烷化合物在溶液中均会在酸催化下从 rctt 形式异构化为 rctc 形式。
