A convenient and efficient synthetic protocol of new selenadiazole and thiadiazoline derivatives incorporating benzopyranone moiety from readily available starting materials was described. Reaction of different 2,2-dialkyl and 2,2-spirocycloalkyl dihydrobenzopyranones 1a–e with semicarbazide hydrochloride and thiosemicarbazide afforded the corresponding semicarbazones 2a–e and thiosemicarbazones 3a–e, respectively. Furthermore, cyclization of the semicarbazones 2a–e via oxidation using selenium dioxide gave a novel series of chromenoselenadiazoles 4a–e. A series of spirobenzopyrano-1,3,4-thiadidazolines 5a–e were synthesized by refluxing of the thiosemicarbazones 3a–e in acetic anhydride. The synthesized compounds were tested in vitro against four cancer cell lines namely: MCF-7, VERO, WI-38, and HEPG-2. In vivo studies were also performed using Ehrlich ascites carcinoma for antitumor activity. Interestingly, Compounds 4b and 5a showed significant antitumor activities and were capable to improve the hematological parameters as well as increase the mean survival time of the mice bearing tumor.