1,5-Dipolar Electrocyclizations of Thiocarbonyl Ylides Bearing CN Groups: Reactions of N-[(Dimethylamino)methylene]thiobenzamide and 2-(Dimethylhydrazono)-1-phenylethane-1-thione with Diazo Compounds
✍ Scribed by Daniel H. Egli; Anthony Linden; Heinz Heimgartner
- Publisher
- John Wiley and Sons
- Year
- 2007
- Tongue
- German
- Weight
- 180 KB
- Volume
- 90
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
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 trans-10d, 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.