The reaction of 2,4‐bis(phenyl)‐1,3‐diselenadiphosphetane‐2,4‐diselenide {[PhP(Se)(μ‐Se)]2, Woollins’ reagent, WR} with N, N‐dialkylcyanamides 1–3 in refluxing toluene solution led to the corresponding [2+3] cycloaddition products 4‐dialkylamino‐2,5‐diphenyl‐1,3,2,5‐selenazadiphosphole 2,5‐diselenides 4–6 in good yields, the latter were further treated with water resulting in the corresponding hydrolysis derivatives dialkyl‐selenoureas 7–9, and phosphinodiselenoates 10 and 11. Selenourea 7 could be transferred into 1,3‐selenazol‐2‐amines 12–15 in excellent yields by further cyclization with four different α‐haloketones. All new compounds have been characterized by IR spectroscopy, multi‐NMR (1H, 13C, 31P, 77Se) spectroscopy and accurate mass measurement. The single crystal X‐ray structural features of nine new compounds are also discussed.