Lawesson s reagent

The product 1s somewhat hygroscopic and should Be stored 1n an airtight container. It Is also available as Lawesson s reagent from Aldrich, Fluka, and from Merck-Schuchard. 

Another reagent system that has been recently employed in the Paal synthesis of thiophenes is the combination of bis(trialkyltin)- or bis(triaryltin) sulfides with boron trichloride. Known as the Steliou reagent,it has been utilized in the transformation of 1,4-diketone 11 to thiophene 12. Higher yields are obtained in shorter reaction times in contrast to the use of Lawesson s reagent. Additionally, others have noted the relative ease of the work-up procedure using the Steliou conditions, and the fact that the tributyltinchloride byproduct of the reaction is reusable. Similarly, the combination of the bis(trimethylsilyl)sulfide has been used in conjunction with trimethylsilyltriflate for the preparation of thiophenes in an analogous manner. ... 

Novel compounds for use in liquid crystal displays have been prepared via the Stetter procedure followed by Paal thiophene formation with Lawesson s reagent. Thus... 

An interesting variation on the Paal thiophene synthesis is observed when applied to an a,p-unsaturated 7-dialdehyde. Thus, treatment of o-phthaldehyde with Lawesson s reagent produced the dithiolactone 36. When 2,3-napthalenedicarboxaldehyde reacted under similar conditions, dithio-2,3-naphthalide 37 was produced in excellent yield. ... 

This 1,3-migration of hydrogen was also observed when 40 reacted with Lawesson s reagent to produce the dithiolactone 41. However, when y-hydroxy-a,P-unsaturated aldehyde 42 was reacted under similar conditions, thiophene 43 was prepared efficiently. These results are not surprising considering that the oxidation state of 42 is equivalent to the traditional saturated 1,4-dicarbonyl substrates of the Paal thiophene reaction via tautomerization of the double bond, and aromaticity is reestablished in the fully conjugated 43. 

Tire first synthesis of 3,4-di-ferf-butyl-l,2-dithiete (172) was performed by treatment of 173 with Lawesson s reagent (LR). Direct thionation of the diketone 174 failed to yield 172 [82JCR(S)314]. 

Although neither of the two carbonyl groups in 18 is immune to the action of Lawesson s reagent,11 it is possible to bring about the selective conversion of the more Lewis-basic lactam carbonyl to the corresponding thiocarbonyl. Thus, treatment of 18 with Lawesson s reagent results in the formation of thiolactam 19 in 85% overall yield from 13. 

Lawesson s reagent 475 f., 738, 742, 746, 752 Lederle 562 lepicidin aglycon 595 f. ligand-accelerated catalysis 681 f. lignane 95... 

Benzoxazepm-5(4// )-onc (2) is converted into 5-chloro-l, 4-benzoxazepine (4) by the action of phosphoryl chloride and into the thione 6 by Lawesson s reagent [2,4-bis(4-methoxyphenyl)-... 

The benzoxazepinedione 1 is selectively thiated at the lactam carbonyl group by Lawesson s reagent to give the one-thione 2.37... 

A similar sequence is assumed for the reaction of 5-chloro-3-phenyl-2,l-benzisoxazole with Lawesson s reagent in toluene, which provides the same product.37... 

The combination of thionation by Lawesson s reagent [98] of oxoenamino-ketones 96 with normal electron-demand Diels-Alder reaction of conjugated aldehydes allows a variety of thiopyrans 97 to be synthesized by a regio-selective and chemoselective one-pot methodology [99] (Equation 2.28). Thionation occurred at the more electrophilic ketonic carbonyl group. O O... 

This conversion may be done indirectly via halogenoquinoxalines (Sections 3.1.1 and 3.2.3), but direct thiation with phosphorus pentasulfide/pyridine or with Lawesson s reagent (43) is less time-consuming. The following examples illustrate typical direct procedures. 

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