1,5‐Dipolar Electrocyclizations of Thiocarbonyl Ylides Bearing CN Groups: Reactions of N‐[(Dimethylamino)methylene]thiobenzamide and 2‐(Dimethylhydrazono)‐1‐phenylethane‐1‐thione with Diazo Compounds

Abstract

The reactions of thiobenzamide 8 with diazo compounds proceeded via reactive thiocarbonyl ylides as intermediates, which underwent either a 1,5-dipolar electrocyclization to give the corresponding five membered heterocycles, i.e., 4-amino-4,5-dihydro-1,3-thiazole derivatives (i.e., 10a, 10b, 10c, cis-10d, and trans-10d) or a 1,3-dipolar electrocyclization to give the corresponding thiiranes as intermediates, which underwent a S N i'-like ring opening and subsequent 5-exo-trig cyclization to yield the isomeric 2-amino-2,5-dihydro-1,3-thiazole derivatives (i.e., 11a, 11b, 11c, cis-11d, and trans-11d). In general, isomer 10 was formed in higher yield than isomer 11. In the case of the reaction of 8 with diazo(phenyl)methane (3d), a mixture of two pairs of diastereoisomers was formed, of which two, namely cis-10d and trans10d, could be isolated as pure compounds. The isomers cis-11d and trans-11d remained as a mixture. In the reactions of the thioxohydrazone 9 with diazo compounds 3b and 3d, the main products were the alkenes 18 and 23, respectively. Their formation was rationalized by a 1,3-dipolar electrocyclization of the corresponding thiocarbonyl ylide and subsequent desulfurization of the intermediate thiiran. As minor products, 2,5-dihydro-1,3-thiazol-5-amines 21 and 24 were obtained, which have been formed by 1,5-dipolar electrocyclization of the thiocarbonyl ylide, followed by a 1,3-shift of the dimethylamino group.1. Introduction. -The concept of the 1,5-dipolar electrocyclization as a tool for the synthesis of five-membered heterocycles has been proposed 25 years ago [1] [2]. Since, we have shown that thiocarbonyl ylides, which bear a C=O group at the C(a)-atom, undergo this cyclization to give 1,3-oxathioles [3] [4] (see also [5] [6]). These thiocarbonyl ylides were generated in situ by the reaction of thiocarbonyl derivatives with a-diazo carbonyl compounds. Very recently, we reported on the reaction of a-thioxocarbonyl derivatives with diazo compounds [7]. We were mostly interested in systems, in which the conjugated p-system consisted of a C=O or a C=S group, i.e., in reactions of a-thioxo ketone 1 and a-thioxo thioamide 2 (Scheme 1).The reactions with diazo compounds 3 all followed the same pathway: 1,3-dipolar cycloaddition to give a 2,5-dihydro-1,3,4-thiadiazole, N 2 elimination by cycloreversion to produce thiocarbonyl ylides 4, and 1,5-dipolar electrocyclization. The resulting products are either 1,3-oxathioles 5 or 1,3-dithioles 6, respectively. Some thiirane side products, which were formed by a competing 1,3-dipolar electrocyclization, were unstable, and elimination of sulfur led to the corresponding alkenes, e.g., 7.

Reactions of thiocarbonyl compounds with electrophilic and nucleophilic carbenes as well as with their metal complexes

“…Microwave-assisted reaction of azibenzil (33) with phenyl thiophen-2yl thioketone (34). The formation of benzoyl phenyl ketene and its subsequent trapping with the cycloaliphatic thioketone 24 was also observed in the reaction of the latter with 2-diazo-1,3-diphenylpropane-1,3-dione (37) while heating at 80°C in toluene Similarly, thermal reactions of thiobenzophenone (25) with differently substituted 2-diazocyclohexane-1,3-diones occurred via a cascade of conversions initiated by the in situ formed diketocarbene.…”

Two Approaches for the Synthesis of Fused Dihydropyridines via a 1,6-Electrocyclic Reaction: Fluorescent Properties and Prospects for Application

“…9−16 The CS bond of a thioamide group may react as a dienophile component in [4 + 2] cycloaddition reactions 17−19 and as a dipolarophile in the thermal and catalytic variants of 1,3-dipolar cycloaddition reactions. 3,20,21 Moreover, α-diazothioacetamides easily transform into 1,2,3-thiadiazoles by a 1,5-electrocyclic reaction. 3,22−25 A specific and significant group of thioamide transformations consists of reactions with acetylenedicarboxylic and propiolic acids and their esters.…”

“…Thioamides are building blocks widely used for the synthesis of nitrogen- and sulfur-containing heterocyclic compounds. − Thioamides can react with various monoelectrophilic, dielectrophilic, and ambient agents, such as α-halocarbonyl compounds and alkyl and alkenyl dihalides. − The CS bond of a thioamide group may react as a dienophile component in [4 + 2] cycloaddition reactions − and as a dipolarophile in the thermal and catalytic variants of 1,3-dipolar cycloaddition reactions. ,, Moreover, α-diazothioacetamides easily transform into 1,2,3-thiadiazoles by a 1,5-electrocyclic reaction. ,− …”