Cycloadditions with 2,2-Dialkyl-3-thioxochroman-4-one S -Sulfides Including an Unprecedented [3 + 5] Cycloaddition
1998; American Chemical Society; Volume: 63; Issue: 26 Linguagem: Inglês
10.1021/jo981534+
ISSN1520-6904
AutoresFarag A. El‐Essawy, Salah M. Yassin, I. EL‐SAKKA, Ahmed F. Khattab, Inger Søtofte, Jørgen Øgaard Madsen, Alexander Senning,
Tópico(s)Synthesis and Catalytic Reactions
ResumoWe report the facile generation of the chroman-4-one-derived thiosulfines 10 under mild conditions by our well-established nucleophilic “unzipping” of the corresponding acetyl α-chloroalkyl disulfides 9 which in turn can be prepared from the corresponding α-chloro sulfenyl chlorides 8. Spontaneous partial loss of sulfur from 10, most probably by the disproportionation of 10 to 11 and 12, generates the expectedly reactive β-oxo thioketones 11 which partly dimerize in a precedented Diels−Alder fashion, to give the 1,3,4-oxadithiins 13, and partly cycloadd to 10 to form the 1,2,4-trithiolanes 14 in a well-precedented fashion. Dimerization of 10 can occur in two competing ways: the precedented nonconcerted [3 + 3] cycloaddition (to give 1,2,4,5-tetrathianes 15) and the unprecedented concerted [3 + 5] addition to give 1,3,4,5,6-oxatetrathiocins 16. In the latter interaction one molecule of 10 behaves as a 1,5-dipole and a second molecule as a 1,3-dipole. In one case (10d) extensive sulfur scrambling takes place with formation of the 1,2,3,4,5,6-hexathiepane 17d. It is remarkable how sensitive the reactions of 10 are to minor variations of the simple alkyl substituents in the 2-position. In addition to the usual spectroscopic characterization all isolated key compounds were subjected to X-ray single-crystal structure determinations.
Referência(s)