A Reagent, Ethyl 2-(2-tert-Butyl-2H-tetrazol-5-yl)-3-(dimethylamino)acrylate (DMTE), for Facile Synthesis of 2,3-(Ring Fused)-5-(5-teratzolyl)-4H-pyrimidin-4-one Derivatives.
A method for synthesizing 2, 3-(ring fused)-5-(5-tetrazolyl)-4H-pyrimidin-4-one derivative from ethyl 2-(2-tert-butyl-2H-tetrazol-5-yl)-3-(dimethylamino)acrylate (DMTE) (4a) and amino-heterocycles is described. The structure of DMTE, which was prepared from ethyl (2-tert-butyl-2H-tetrazol-5-yl)acetate (3a) with dimethylformamide diethylacetal, was determined by X-ray analysis to be Z form. The reaction of 2-amino-5-methyloxazole (6) with DMTE in acetic acid gave the oxazolo[3, 2-a]pyrimidine derivative (8), heating of which in concentrated sulfuric acid afforded the desired tetrazole derivative (20). Pyrimido[2, 1-b]benzothiazole (21), pyrazolo[1, 5-a]pyrimidine (22 and 23) and [1, 2, 4]triazolo[1, 5-a]pyrimidine (24) derivatives were prepared in a similar manner.
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。