E ¼ Se: 2a 2b 2c ð1Þ however, reacted immediately with tert-butylnitrite or with NOCl even at À788C furnishing deep-red solutions that become brownish within 1–2 h at À788C or within a few minutes at room temperature; this decomposition led to diselenide 2 c. It turns out that nitrosation products 3b and 4b carrying the extremely bulky trisyl substituents are significantly more stable than 1b and 2b [Eqs.(2) and (3), Tsi=(Me3Si) 3C].