In the context of this Diploma work, syntheses of some 2H-pyran-2-ones are presented. Additionally, an example of the replacement of a protecting group on a selected 2H-pyran-2-one and the synthesis of a byciclo[2.2.2]octene adduct prepared from maleic anhydride and 3-benzoylamino-6-(2-thienyl)-2H-pyran-2-one are included. The latter was performed in two different ways - under reflux conditions and by using irradiation with microwaves. The purpose was to determine whether both paths would lead to the desired end product and to find out which path would result in a better yield. This Diploma work also presents the literature data on regio- and stereoselectivity of [4+2] cycloadditions, in which 2H-pyran-2-ones are often represented as diene compounds. Due to the unique characteristics of 2H-pyran-2-ones, these reactions represent an extremely powerful synthetic tool for the formation of more complex molecules and structurally extremely diverse synthetic building blocks.