Compounds of formula I wherein R1, R2, R3, R4 and R5 have the means set forth in the description are selective cyclic nucleotide phosphodiesterase (PDE) inhibitors (specifically of type 4), which are effective bronchial therapeutics.
tetrazole (1,5-Tz) in several cases. The regioselectivities (1,5-Tz:2,5-Tz) are highly variable and cannot be exclusively attributed to the steric hindrance of the electrophile. A new rationale to explain the observed regioselectivity, based on the difference in mechanism between first- and second-order nucleophilic substitutions, is thus proposed. In addition, in some cases the intramolecular stabilization
二取代四唑的合成描述了从 1 H -5-单取代四唑通过脂族胺重氮化反应,形成瞬时烷基重氮中间体,充当烷基化剂。尽管 2,5-二取代四唑 (2,5-Tz) 以中等至极好的收率优先形成,但在几种情况下也可以分离出少量的 1,5-二取代四唑 (1,5-Tz)。区域选择性(1,5-Tz:2,5-Tz)是高度可变的,不能完全归因于亲电试剂的空间位阻。因此,基于一级和二级亲核取代之间的机制差异,提出了解释观察到的区域选择性的新原理。此外,在某些情况下,所得重氮的分子内稳定性会影响区域选择性。