Synthesis from isothiocyanates

The trisubstituted amidinothioureas (98) required as precursors of the thiadiazolines are obtained by the interaction of isothiocyanate esters and s-diarylguanidines,115 or by the action of aromatic amines on dithiazolidines (102).117 The former reaction might conceivably yield the isomeric amidinothioureas (98a) instead if so, however, oxidation and isomerization would give rise to a 2-(diphenylguanidino)benz-thiazole (100a) isomeric with, but different from, the product (100) actually obtained. The structure of this product is confirmed by synthesis from 2-aminobenzthiazole (101) and carbodiimides.115... 

The availability of amino-substituted furazans, both by direct synthesis from aminogly-oximes and via Hofmann degradation of the corresponding carboxamides, allows urea, thiourea, imino and acylamido derivatives, for example, to be prepared by reaction with isocyanates, isothiocyanates, aldehydes and acyl halides, respectively (73JPR791, 77JCS(P1)1616). Alkoxy and acyloxy derivatives are likewise formed from hydroxyfurazans (79JHC689). 

I. Ugi (ed.), Isonitrile Chemistry. Academic Press, New York, 1971. Synthesis of heterocycles, from isothiocyanates ... 

Similarly, from the same laboratory, a new and practical procedure for synthesis of isothiocyanates was described. They were readily obtained from the corresponding isocyanates using Lawesson s reagent under the action of MW irradiation and solvent-free conditions [190] (Eq. 32). Important specific not purely thermal MW effects were measured accurately here. Because thionation has been described to occur via a polar transition state reaction [191], it is expected to be accelerated under the action of MW irradiation this could explain the significant rate enhancement. 

Table 3.20 Thiourea Synthesis From Amines and Isothiocyanates ...

Synthesis.—From Thid)carbamoyl Isothiocyanates. Carbamoyl isothiocyanates and thiocarbamoyl isocyanates are thermally interconvertible X-CS NCO X CO NCS.i2 In an extensive study of the preparation and chemical behaviour of these reagents, their use in heterocyclic synthesis was evaluated. 2 ... 

Carbamoyl isothiocyanates (6) similarly afford 40—60% yields of substituted 1,2,3-thiadiazoles of type (7), the structure of which is confirmed by an independent synthesis from the appropriate urethane (8). 

Amino-thiazole synthesis from a-aminonitriles and carbon disulfide, or carbon oxysulfide, isothiocyanate, dithioacids. 

Willis et al reported an enantioselective direct aldol reaction for the synthesis of protected aryl P-hydroxy-a-amino acids catalyzed by chiral Mg (I I) complexes (Scheme 4.12) [12]. A catalyst system composed of 10 mol% of Mg(Cl04)2,11 mol% of (S,S)-Ph-Pybox (35), and diisopropylethylamine generated an enolate of a chiral glycine equivalent derived from isothiocyanate-substituted oxazolidinone (33). The... 

K A L U Z A Isothiocyanate synthesis Formation of isothiocyanates from amines. 

The synthesis of 987 from 985 via 986 has been reported (83S759) by reaction of 985 with aryl isothiocyanates under neutral conditions. The reaction of 4-amino-6-anilino[l,2,4]triazine 988 with methyl iodide and then carbon disulfide gave 989 (90MI3, 90MI9). 

The second approach for the synthesis of 2-amino-3-hydroxycarboxylic acids starts with a chiral isothiocyanate which is added, via the tin enolate, to aldehydes. The initially formed adducts are immediately derivatized to the heterocycles, from which. yj 7-2-amino-3-hy-droxycarboxylic acids result after a three-step procedure. The diastereomeric ratios of the intermediate bis-heterocyclic products range from 93 7 to 99 1 (desired isomer/sum of all others)104. 

Glutaconaldehyde anion serves as an interesting intermediate for the synthesis of heterocyclic compounds. The parent pyrylium perchlorate has been prepared from glutaconaldehyde and 70% perchloric acid in ether at -55°.° The reaction of glutaconaldehyde anion with alkyl and aryl isothiocyanates and... 

Organic synthesis 13 [OS 13] Thiourea from phenyl isothiocyanate and cyclohexylamine... 

OS 13] [R 17] [no protocol] Using a micro mixer/commercial tube reactor, the synthesis of a thiourea from phenyl isothiocyanate and cyclohexylamine at 0 °C was carried out [85] (see a more detailed description in [42]). A single mixing device connected to a stainless-steel tube of about 10 m length and 0.25 mm diameter was used. The feasibility of performing a nearly spontaneous reaction could be shown. 

Scheme 13 depicts the synthesis of compound 144 containing the isothiocyanate at both terminal positions prepared from the highly fluorescent tetramer 141 (Scheme 13) <2003JOC1512>. 

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