This thesis describes the synthesis of new heterocyclic derivatives with an ultimate goal of exploring new procedures for the synthesis. This co-supervise research was carried out under the Channel Scheme between school of Pharmacy in Zagazig University and School of Chemistry in Cardiff University. Chapter one: this chapter contains an investigation for the synthesis of novel 1,2,4-triazine derivatives. The synthetic strategy depends on incorporation of various carbon-based substituents into a 4-amino-3-thioxo-1,2,4-triazine nucleus by a straightforward thermal Claisen rearrangement that was also modified by using a related palladium-catalysed method which was found to be more efficient. It also displays the synthesis of a series of 1,2,4-triazine-3,5(2H,4H)-dione derivatives via a high-yielding acid-catalysed rearrangement procedure. Chapter two: this chapter aimed to utilise the acid-catalysed hydroamination to synthesise tetrahydroisoquinolines from suitably substituted benzhydryl derivatives. The used methodology represents an alternative to the classical Pictet-Spengler synthesis of tetrahydroisoquinolines as it outlines a scheme of few steps to the benzhydryl derivatives that were cyclised under mild acidic conditions and offer the 1-aryl- and 1-heteroaryltetrahydroisoquinoline derivatives. Chapter three: this chapter focuses on extending the synthetic route used in chapter two to provide phthalazine analogues by incorporating hydrazine functionalities rather than using protected amines. Mitsunobu protocols were used successfully to deliver the targeted hydrazine precursors. On the other hand, Suzuki couplings of the obtained precursors with different boronic acids and esters allow the synthesis of a series of vinylbenzyl hydrazine derivatives which underwent successful hydroamination reactions into the corresponding tri-substituted phthalazine derivatives. Chapter four: this chapter describes silver-catalysed cyclisations, it involves 5-endo-dig cyclizations of a small series of alkyne-diols derived from large carbocycles in order to synthesize furan derivatives with macrocyclic structures that could be useful in the fragrance industry. The proposed furan derivatives were obtained in quantitative yields and without any need for purification.