LAWESSON Thiocarbonylation Reagent

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. 

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... 

The reaction now is frequently carried out using the Lawesson s reagent. For the mechanism of carbonyl to thiocarbonyl transformation, see Lawesson s reagent on page 348. 

This is often achieved from 1,4-dicarbonyl compounds in a procedure similar to that used to form furans but using phosphorus pentasulfide, or Lawesson s reagent (see below), to cause a transposition from carbonyl to thiocarbonyl groups, prior to cyclization and loss of hydrogen sulfide (Scheme 6.37). 

Dihydrobenzoxazin-3-one 20 and its A -methyl derivative 165 can be converted into the corresponding thiocarbonyl compounds 166 and 167 using Lawesson s reagent <1988M1439> or phosphorus(v) sulfide <2005H(65)579> (Equation 9). 

The reduction of 114 with LAH, followed by reaction with triphosgene, led to benzo[l, 2,5]thiadiazepin-6(4//)-one 1,1-dioxide 115, which upon treatment with Lawesson s reagent gave the corresponding thiocarbonyl derivative 116 (Scheme 26). The 1,2,5-thiadiazepine 115 was acylated by treatment with di-/-butyldicarbonate in the presence of AyV-dimethylaminopyridinc to afford 117, which is alkylated with 3-methyl-2-butenyl bromide or ethyl iodide to give 118 and 119, respectively <2002JHC81>. 

Partially and perfluorinated thioketones and thioaldehyde were stabilized as anthracene adducts (70). The adducts (70) were prepared in moderate yield from the corresponding carbonyl compounds with P4S10 or Lawesson s reagent in the presence of anthracene under toluene reflux. The generated thiocarbonyl compounds are not accessible in bulk due to their tendency towards polymerization. By thermolysis of the anthracene adducts (70) in the presence of C,N-bis(triisopropylsilyl)nitrilimine (NI), 1,3,4-thiadiazole derivatives (71) were obtained. Also, 1,3-dipolar cycloaddition with bis(trimethylstannyl)diazomethane (BTSD) to give consecutive products (72) from a 1,2-metallotropic migration of primary adducts was discussed. [95LA95]... 

As a unique reaction, treatment of thionoesters (41) or thionolactones with Ph3SnH in the presence of Et3B at room temperature provides the reduction products (42) of thiocarbonyl groups to methylene groups (eq. 7.19) [44, 45]. Thus, this is the indirect reduction of esters to ethers, and lactones to cyclic ethers, since thionoesters and thionolactones are prepared from the corresponding esters or lactones with Lawesson s reagent. 

Lawesson s reagent [2,4-bis(4-methoxyphenyl)-2,4-dithioxo-/)V,Pv-1,3,2,4-dithiaphosphetane] is a versatile and efficient reagent for the conversion of carbonyl to thiocarbonyl derivatives in boiling toluene.12 While the high temperature required prevents the use of this method for thermally unstable thioacylsilanes, the more stable derivatives have been prepared in excellent yields (Table 3, Scheme 3). 

Another example of conversion of a carbonyl into a thiocarbonyl is provided by dibenzodiazocinone 32 which, upon reaction with Lawesson s reagent, furnished the dithiocarbonyldiazocine 33 in 91% yield <2004JOC1248>. 

Cyclopropyl ketones and lactams as well as amides of cyclopropanecarboxylic acids were converted to the corresponding thiocarbonyl compounds on reaction with 2,4-bis(4-methoxyphenyl)-l,3,2,4-dithiadiphosphetane-2,4-dithione (Lawesson s reagent) in benzene or toluene the yields were good. For example, reaction of lactam 1 to give thione 2. Thiones were also formed when hydrazones were treated with sulfur monochloride. ... 

A solution-phase reagent commonly employed for the transformation of carbonyl groups to thiocarbonyl analogues is Lawesson s reagent, which con-... 

Important reactions have included sulfur as nucleophile and leaving group in the 5 2 reaction (illustrated here see also Chapter 17), sulfonation of aromatic rings (Chapter 22), formation and reduction of thioacetals (Chapter 24) and Lawesson s reagent for converting carbonyl groups to thiocarbonyl groups (Chapter 44). 

The nucleophile is the same in both cases and it is an odd-looking molecule. That is, until we realize that it is just a tautomer of a thioamide. Far from being odd, thioamides are among the few stable thiocarbonyl derivatives and can be easily made from ordinary amides with PzSj or Lawesson s reagent. 

Lawesson s reagent converts carbonyl groups into thiocarbonyl groups (For the mechanism of conversion of carbonyl into thiocarbonyl with LR and reviews of LR... 

Diaryl-substituted bi(thieno[3,4-b]thiophene)s 156 were generated by intramolecular double 5-exo-dig cyclizations of bis[(aiylthiocarbonyl)thien-2-yl]acetylenes 155 [58]. For example, the reaction of 154 with Lawesson s reagent in refluxing toluene led to thiocarbonyl compound (155), thermal 5-exo-dig cycliza-tion of which furnished 156 in 82% yield (Scheme 35). 

In the last decade the methods of converting carbonyl to the corresponding thiocarbonyl compounds have been substantially improved. " Therefore, thioxo- as well as dithio-carboxylic esters are accessible from esters, thiol esters and even carboxylic acids by reacting them with phosphorus pentasul-fide or 1,3,2,4-dithiadiphosphetane 2,4-disulfides such as Lawesson s or Davy s reagent (equation 4 cf. Chapter 4.1, this volume). 

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