Less reactive dipoles of diazodicarbonyl compounds in reaction with cycloaliphatic thioketones – First evidence for the 1,3-oxathiole–thiocarbonyl ylide interconversion

Abstract

SummaryAcyclic diazodicarbonyl compounds react at room temperature with cycloaliphatic thioketones, e.g. 2,2,4,4-tetramethyl-3-thioxocyclobutanе-1-one and adamantanethione, via a cascade process in which the key step is a 1,5-electrocyclization of the intermediate thiocarbonyl ylide leading to tetrasubstituted spirocyclic 1,3-oxathioles. The most reactive diazodicarbonyl compound was diazoacetylacetone. In the case of dimethyl diazomalonate competitive 1,3-electrocyclization yielded the corresponding thiirane at elevated temperature, which after spontaneous desulfurization produced a tetrasubstituted alkene. To explain the observed temperature dependence of the main reaction product type obtained from dimethyl diazomalonate and 2,2,4,4-tetramethyl-3-thioxocyclobutanе-1-one as well as to verify reversibility of the thiocarbonyl ylide and 1,3-oxathiole interconversion, the calculations of the energy profile for the transformation of 1,3-oxathiole to alkene were performed at the DFT PBE1PBE/6-31G(d) level.

1,3‐Dipolar Cycloadditions of α‐Diazo Ketones Derived from N‐Protected (S)‐Proline with Aromatic and Cycloaliphatic Thioketones

“…Apparently, the hetaryl substituents are decisive for the 1,3-dipolar electrocyclization and the subsequent elimination of S. The replacement of the hetaryl groups by Ph leads to the alternative 1,5-dipolar electrocyclization of the intermediate thiocarbonyl ylide 4. In contrast to some other 1,3-oxathiols [3], the products 6 do not undergo isomerization via ring opening to form thiiranes in solution.…”

“…The analogous signal of the minor rotamer appeared at 5.58 ppm. The structure of a 1,3oxathiole was additionally supported by the 13 C-NMR data, and the signals detected at 103.4 and 102.8 ppm for the major and minor rotamer, respectively, are of special importance [3] [10]. Furthermore, the ESI-MS provided the molecular formula C 26 H 23 NO 2 S (m/z 436 ([M þ Na] þ )).…”

“…Reactions of thioketones 1 with diazoalkanes are especially important, as the [3 þ 2] cycloadducts formed can be isolated in some instances and subsequently used for the generation of reactive thiocarbonyl ylides [2]. It is well-known that a-diazocarbonyl compounds 2 are less reactive and, for that reason, their reactions with thioketones must be carried out at enhanced temperature [3] or/and in the presence of a catalyst such as LiClO 4 [4] or Rh 2 (OAc) 4 [4] [5]. Characteristically, reactions with a-diazocarbonyl compounds 2 occur with spontaneous elimination of N 2 from the initially formed cycloadducts 3, and the intermediate thiocarbonyl ylides 4 undergo competitive 1,3-dipolar or 1,5-dipolar electrocyclizations [6] (Scheme 1).…”

“…Among cycloaliphatic thioketones (cycloalkanethiones), adamantanethione (1f) and 2,2,4,4-tetramethylcyclobutane-1,3-dithione (1g) are favorite model compounds, which are frequently used to study the reactivity of the C¼S group [12]. In comparison to other a-oxo diazo compounds [3], the reaction of 1f with 8a and 8c in boiling THF occurred smoothly with evolution of N 2 . The chromatographic workup led to only one product in each case, identified as the corresponding 1,3-oxathiols 6d and 6e, respectively (Scheme 5).…”

“…Thiobenzophenone (¼ diphenylmethanethione; 1a), the symmetrical heteroaromatic thioketones 1b, 1c, and 1d, and the nonsymmetrical heteroaromatic thioketone 1e were obtained from the corresponding ketones as described in [11]. Adamantanethione (¼ tricyclo[3.3.1.1 3,7 ]decane-2-thione; 1f) and 2,2,4,4-tetramethylcyclobutane-1,3-dithione (1g) were prepared from the corresponding ketones as described in [12]. Other reagents used in the present study were commercially available.…”