Lawesson thionation

Cyclic ethers from lactones. The ready addition of RLi to the C=S group of thionolactones (14, 9) has been used to prepare functionalized cyclic ethers from lactones of the same ring size. The first step involves Lawesson thionation of lactone... 

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]. 

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... 

In addition, thionation-cyclisation of 1,2-diacylhydrazidines to 1,3,4-thiadiazoles has been achieved by the action of Lawesson s reagent under solvent-free microwave irradiation in a domestic microwave oven (Scheme 21). This ring-closure methodology was extended for the synthesis of various liquid crystals [1]. 

Dithio-squaraines 37 can be synthesized via thionation of the correspondent oxo-squaraines 5 with phosphor pentasulphide or Lawesson reagent (Fig. 8) [103, 104], However, dithio-squaraines containing carboxylic groups cannot be obtained by this method. Symmetrical indolenine- and benzothiazole-based monothio- (38) and dithio- (37) squaraines containing carboxy and sulfo groups are synthesized using 1,2-dithio- and tetrathiosquaric acid, respectively, while the reaction of these... 

This ring system could be prepared by thionation of benzil monohydrazone 172 with Lawesson s reagent (LR) followed by cyclization. The reaction gives 2,3-diphenyl-7,8,9,9a-tetrahydro-27/,677-pyrido[2,TA][l,3,4]thiadiazine 173 in a diastereoselective way, with the hydrogens at 2- and 9a-position in trans orientation. Benzil monohydrazone 172 was obtained by condensation of benzil 170 with 1 equiv of iV-aminopiperidine 171 (Scheme 23) <1998TA1531>. 

The conversion of a carbonyl to a thiocarbonyl group, or thionation , is a common procedure for the synthesis of thioketones. Several methods that use P4Sio,49 51 Lawesson s reagent (L.R.),2 52 57 H2S,58 59 NaHS,60 or hex-amethyldisilathiane (HMDST)61,62 are described. L.R. and P4S10 have been used to sulfurate partially and entirely perfluorinated carbonyl compounds,63 which are then trapped as anthracene adducts in a one-pot reaction. H2S has... 

Direct thionation of amino acid derivatives has been achieved using P4S10. Direct thionation of anilide has been achieved with a mixture of P4S10 and anhydrous Na2C03 in THF.19 Selective thionation of amide has been achieved using P4S10 in THF under ultrasound irradiation. By-product is absent from the phosphorus pentasulfide thionation. Thionation of the amide with Lawesson s reagent is less selective (Scheme 4).20... 

Recent advances in the use of Lawesson s reagent include its application in microwave assisted solvent-free syntheses, solid-phase synthesis and combinatorial chemistry.165 Despite the ubiquity of Lawesson s reagent for organic thionation reactions, there are still some classes of compounds that it does not... 

Bridging of macrolides.1 A number of natural products are known to consist of oxapolycyclic systems. A potential route to such systems involves bridging of the more readily available macrolides (or the corresponding dithionolides, available by thionation with Lawesson s reagent) by electron-transfer reactions initiated with sodium naphthalenide (Scheme I). 

Finally Ebersbach s group succeeded in synthesizing the first (and, up to now, only known) authentic pyrido[l,2-a]azepine base 315 (Scheme 70) from their lactam 290 by thionation with Lawesson reagent (LR), methylation of thiolactam 313, and deprotonation of sulfenium salt 314 (91HCA1095). 

Thionation of 3-Wacylamino ketones with Lawesson s reagent (LR) gives the 3-Wthioacylamino thiones which cyclize to the 1,3-thiazines 216 with loss of H2S (Equation 20) <2000H(52)111, 2001HGA2347>. 

Diol 74 reacts with 4equiv of l,l -thiobisbenzimidazole 146 in acetonitrile at room temperature to afford a diastereomeric mixture of thionosulfites 3c and 3d in the ratio 82 18. Attempts to make 3c or 3d by thionation of 3a or 3b using Lawesson s reagent were unsuccessful (Equation 26) <2003JA9024>. 

Similar to Lawesson s and Daw s reagents. Used as a mild thionation reagent for esters and lactones. 

The catalysed reaction of hydrogen sulfide on ketones or their acetals, or the thionation of carbonyl derivatives by tetraphosphorus decasulfide, or some modified version of this phosphorous compound as Lawesson, Davy and Heimgartner reagents are classically used [119, 120] to prepare the thioketones (2). 

The thionation of esters and thiolesters by thiophosphorus derivatives and mainly by Lawesson s reagent is another general process (Table 2.2) [136,137]. 

Again in the field of natural products synthesis, Lawesson reagent has found application in the obtention of sulfur carotenoids285 (equation 39) and thionated steroids286 (equation 40). 

The versatility and selectivity of the Lawesson reagent is also evidenced in the synthesis of the highly complex alkaloid 19-hydroxytubotaiwine287, in which a ketolactam is transformed into a thionethiolactam (equation 41). Also, Diels-Alder cycloadducts can be thionated with 52 and, upon thermolysis at high temperatures (FVT), afford the corresponding thioketenes which are trapped in situ2m (equation 42). 

A different strategy has been the utilization of organometallics, such as acylferrocenes, as stabilizing groups in thionation reactions either with P4S10395 or with Lawesson reagent396 (equation 101). 

Substitution of the phosphinate ester group by dimethylamine via the chloride, and thionation of the P=0 group of the 2-phosphabicyclo[2.2.2]octane P-oxide derivatives 28 with diphosphorus pentasulfide affords the corresponding amide 29 and P-sulfide 30 (Scheme 10). The thionation is also achieved with Lawesson s reagent [7,8]. Thermolysis of 28 proceeds a retro Diels-Alder reaction to give 31. 

Scheme 62 Thionation of 192 with Lawesson s reagent to give the corresponding cyclic thiophosphate 194...

Lawesson s Reagent is a mild and convenient thionating agent for ketones, esters, and amides that allows the preparation of thioketones, thioesters and thioamides in good yields. 

Lawesson s reagent (LR) is a very effective thionating agent of carbonyl compounds. However, attempted thionation with LR of iV-alkylhydroxamic acids gave maximum yields of 55-60%. Previous work had established that the thionation products, the thiohydroxamic acids (THA), were accompanied by the corresponding amides (A) formed by reduction and the thioamides (TA), the products of thionation of the amides (A) (Scheme 16). Now the reaction of (V-isopropylhydroxamic acid (HA R = IV) with LR has been followed by 31P NMR spectroscopy and several P-containing intermediates have been identified. This has permitted the delineation of a rational, but complex, pathway to each of the products of the reaction.45... 

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