No abstract

We 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.

The reaction of 1 a, b with cyclohexanone afforded hexahydronaphthalene derivatives (3 a, b). In contrast to the behaviour of 1 a, b, cyclohexanone reacts with 4a–c to yield the propenylidenecyclohexanone derivatives (5a–c). The reaction of 1a with acetylacetone gives 4H‐pyran 6 and a 1:2‐adduct 8 a. On treatment of 8 a with sodium metal in the presence of dioxane, the pyrano [2, 3‐b]pyridine (9a) was obtained. When 1 b, c reacted with acetylacetone, the only isolable products were 8 b,c. Reaction of 4a with acetylacetone gives acyclic compound 10. This on treatment with basic reagents, gives the pyran derivative (13).

The reaction of ethyl 2-arylhydrazono-3-oxobutyrates (Ia, Ib) with active methylene ketones afforded pyridazin-5-carbonitrile derivatives. The methyl function in the ethyl pyridazin-3-carboxylate derivatives IIa, IIb reacted with arylidenemalononitrile to yield the phthalazine derivatives Va-Vf and with elemental sulfur to yield the thienopyridazines XIXa, XIXb. The cinnolines are producted from reaction of IIa, IIb with diethyl acetonedicarboxylate.