Thioamides rearrangement

Diastereoselective asymmetric thio-Claisen rearrangement has been carried out by the reaction of thioamides with allyllic bromide (Scheme 37).76... 

C, and then three molecular equivalents of acetyl chloride and triethy-lamine were added. Three types of acetylated materials, 11, 12, and 13, were isolated accompanied by a small amount of thioketone 7 and thioamide 9 (Scheme 8 and Table 6). All of the acetylated materials showed optical activity. For the reaction of 6a, 84% ee of 2-(acetylthio)aziridine 11a, 50% ee of 4-(acetyl-thio)oxazoline 12a, and 20% ee of 4-(acetylthio)oxazolidin-2-one 13a were obtained in 39,10, and 16% yields, respectively. In the reaction of 6b,c, the corresponding optically active materials 11-13 were obtained as shown in Table 9. The formation of oxazoline 12 involves the rearrangement ofAT-acyl aziridines, which occurs by intramolecular attack of the carbonyl oxygen at the ring carbon to cause rupture of the system. 

Thieno[4,3,2-/g]benz[l]azocine 187 is produced in high yield (79MI397) from oxime 186 by Beckman rearrangement in PPA. Transformations of amide and thioamide groups of azocines 187 and 188, lead to derivatives 189-192, as shown in Scheme 52. 

Thioamide formation benzodiazepinone, 505 heteiodiazepinone, 621 phosphorus pentasulf ide, 323, 600 Thioazole formation, nitrile addition, 301 Thiocarbamate formation, 588 phenol, 95 rearrangement, 517 Thioenol ether formation, 185, 517 addition-elimination, 554 Thioester formation, mixed anhydride, 184 Thioether formation, 241, 300, 413, 416 alkylation, 586, 588 aromatic displacement, 416 Thiohydantoin formation, 293 Thiol interchange, benzothiazole formation, 422... 

The initial step of this condensation appears to be the attack of the primarily formed imidochloride R—C( NH)C1 (or [R—C=NH+]C1 ) at the sulfur of the thioamide. The resulting diimido-sulfide (77) then rearranges irreversibly to the more stable end-product (78),presumably via an intermediate cyclic stage.108... 

Reactions of alkynyliodonium salts with multidentate nucleophiles can be employed for the synthesis of heterocyclic compounds. Recent examples include preparations of thiazoles, selenazoles, and 2-mercaptothiazoles by the treatment of alkynyliodonium mesylates or tosylates with thioamides, selenoamides, and ammonium dithiocarbamate (Scheme 62) [169-171]. A novel hetero-Claisen rearrangement of tricovalent iodine(III) intermediates was proposed to account for the 2,4-disubstitution pattern of the thiazoles [169]. 

Alkynyl( aryl) iodine (I II) compounds 89 can also be employed in hetero-Claisen rearrangements [151] after reaction with appropriate thioamides yielding thiazoles of type 90 in reasonable yields as shown in Scheme 38 [152]. Ring enlargement reactions of furan derivatives into pyranones by hypervalent iodine compounds were reported as well [153]. 

Various 2-substituted iV-phenyl-6-phenylimino-3,6-dihydro-2//-thiopyran-4-amines, which are available from 6-substitutcd-5,6-dihydro-2//-thiopyran-2-thioncs, thermally rearrange to 5,6-dihydropyridine-2(l//)-thiones. A resonance stabilized thioamide anion is proposed as the intermediate (Scheme 107) <2001T8305>. 

The aldol reaction of dithioester enethiolates has been used for the synthesis of dithiolactones [123], chiral substrates for the Claisen rearrangement [124, 125], and oxathianes [126]. Thioamide enethiolates may be employed in this reaction as well as shown with /Tthiolactams [26], or with a precursor of the antitumour agent vinblastine [127]. 

The thio-Claisen rearrangement can also be performed with secondary thioamides, providing allylation on the nitrogen atom rather than carbon atom. An elaborate example was reported by Fuchs and Smith [183]. They introduced an allyl ammonium salt to achieve SN2 alkylation of sulfur, and the product readily rearranged to furnish the expected thiolactam. However they finally preferred to employ in the first step an allyl mesylate, which was more easily synthesised. 

The rearrangement of S-allyl thioimidates to Al-allyl thioamides requires a catalyst because of double bond isomerization and deallylation during the thermal reaction. Palladium(II) salts, but not mercury(II) salts catalyze these reactions efficiently and selectively under mild conditions (see Table 5, entries 1-3). Cationic intermediates similar to those discussed for the allylimidate rearrangement are proposed61 63. Studies with nonracemic thioacetimidates have not been reported. 

Base-induced S-allylation of dithioesters [17,18], thionoselenoesters [19] as well as tertiary thioamides [20-23] with allylic halides and alcohols [24] have been commonly used to generate S-allyl ketene-S,W-acetals (W = S,Se, N), which are prone for a thio-Claisen rearrangement. In fact, the marked trend of the starting thiocarbonyl compounds to render the cis-... 

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