Syntheses of 4-Selenazolones. Hetero Diels-Alder Reaction of the Selenazadienes with DMAD

Synthesis of selenoureas and heterocycles based thereon

“…Selenazadienes 22 were synthesized in 75-98% yield by condensation of N,N-disubstituted selenoureas 14 with 1.5 equiv of N,N-dimethylformamide dimethyl acetal at room temperature [88][89][90]. Selenazadienes 26 can also be obtained in a very high yield by reaction of stable N-phenyl-and N-benzylimidoyl isoselenocyanates 25 with ammonia or primary or secondary amines [91][92][93][94].…”

“…During silica gel purification, intermediate six-membered Diels-Alder adducts 79 underwent rearrangement into five-membered selenadiazoles 81. The rearrangement is likely to involve protonation of 79 and opening of the six-membered ring with formation of selenoamidine 80 whose cyclization yields 81; hydrolysis of the latter leads to 1,3-selenazol-4-one 82 [88]. Unlike N,N-disubstituted selenoureas 14 carbonyl chlorides 84 which were treated with water, alcohols, or amines [120,121] (Scheme 24).…”

Facile synthesis of 4H-naphtho[2,3-e] derivatives of 1,3-thiazines and 1,3-selenazines and naphtho[2',3':4,5] derivatives of selenolo[2,3-b]pyridines and thieno[2,3-b]pyridines via 2,3-didehydronaphthalene

“…One of the referees of this paper suggested the possibility that the electrons in 12 flow the other way in which the heterocyclic ring is reduced to 14 and the dimethylamine moiety is oxidized to CH 3 N=CH 2 (15). This possibility is illustrated in Scheme 4.…”

“…13 The thiaazabutadienes (2a-e) 14 and the selenoazadienes (6a-f) 15 were prepared by literature procedures. With the exception of thiaazadiene (2e) the thiaazadienes (2a-d) are new compounds and their % yields are shown in Scheme 1.…”

Dimethylformamide dimethyl acetal as a building block in heterocyclic synthesis

“…Interestingly, the reaction did not give the expected Diels-Alder adduct but a mixture of E/Z isomers of (202) was obtained. The reaction was carried out as shown in Scheme 29 [141]. The reactivity of the N-selenoacylamidine (201e) as 4p heterodienic system in [4 þ 2] cycloaddition reactions with electrophilic dienophiles was investigated.…”