Ring-opening/ring-closing protocols from nitrothiophenes: six-membered versus unusual eight-membered sulfur heterocycles through Michael-type addition on nitrobutadienes.
When Ar is a low-aromaticity homo- or heterosystem, the sulfonyl-stabilized anion of nitrobutadienes 4 (which derive from the initial ring opening of 3-nitrothiophene) undergoes a rather surprising addition onto the aromatic ring itself, thereby leading to the construction of an unusual eight-membered sulfur heterocycle condensed with the original Ar ring. The competitiveness of such a pathway with respect to the formation of the thiopyran ring (i.e., addition onto the nitrovinyl moiety) is favored at low temperatures, thus revealing its nature as a kinetically controlled process.
Bianchi
Lara
L
Dipartimento di Chimica e Chimica Industriale, Genova University, Via Dodecaneso 31, 16146 Genova, Italy.
Giorgi
Gianluca
G
Maccagno
Massimo
M
Petrillo
Giovanni
G
Sancassan
Fernando
F
Severi
Elda
E
Spinelli
Domenico
D
Stenta
Marco
M
Tavani
Cinzia
C