Imino thioethers

A -Imidazolines (294 Z = NH) are cyclic amidines and exhibit the characteristic resonance stabilization and high basicity. A -Oxazolines (294 Z = 0) are cyclic imino ethers, and A"-thiazolines (294 Z = S) are imino thioethers both are consequently easily hydrolyzed by dilute acid. 

If the rearrangement of oxime sulfonates is induced by organoaluminum reagents,the intermediate (71) is captured by the nucleophile originally attached to the Al. By this means an oxime can be converted to an imine, an imino thioether (R—N—C—SR), or an imino nitrile (R—N—C—In the last case, the nucleophile comes from added trimethyl si lyl cyanide. The imine-producing reaction can also be accomplished with a Grignard reagent in benzene or toluene. ... 

Imino thioethers,2 The reagent, prepared in situ, converts the dimethyl thioketal of a cyclic ketone (2) into the imino thioether 3 in high yield. The reaction can also he carried out with azidotrimethylsilane (1 equivalent), stannic chloride (1 equivalent), and iodine (10 mole %). but yields arc lower. This reaction was examined because of the reaction of thiokctals with iodine azide (this volume). 

When 188 (X = Cl) was heated in acetic acid either with or without one equivalent of sodium acetate, the isoquinoline (189) was formed. The free base 190 of 188 could be isolated by neutralization with mild alkali and, as with most imino thioethers, slowly reverted to... 

Trost, B. M., Vaultier, M., Santiago, M. L. Thionium ions as carbonyl substitutes. Synthesis of cyclic imino thioethers and lactams. J. Am. Chem. Soc. 1980,102, 7929-7932. 

Tertiary amines from thioamides. Alkyldichlorocerium reagents (alkyl group being primary) react with imino thioethers, which are formed by treatment of thioamides with MeOTf. 

Biomimetic Cu(II) and Fe(II) complexes with bis- and tris-pyridyl amino and imino thioether ligands and vacant (or potentially so) coordination positions (Fig. y are active as catalyst precursors for the solvent- and halogen-free MW-assisted oxidation of 1-phenylethanol by TBHP, in the presence of pyridazine or other N-based additives. Maximum TOF of 5220 h (corresponding to 87% yield) was achieved just after 5 min of reaction time under the low power MW irradiation. The same authors reported" the catalytic activity of related copper, iron, and vanadium systems with mixed-N,S pyridine thioether hgands. The Cu and Fe complexes proved to be useful catalysts in various MW-assisted alcohol oxidations with TBHP, at 80 °C. Thus, 5-containing ligands can also be used to create effective catalyst precursors. 

Figure 1 Iron and copper complexes with bis- and tris-pyridyl amino and imino thioether ligands. ...

Several recent examples use copper(II) or Cu(II)/TEMPO catalytic systems, namely alkoxy-l,3,5-triazapentadien(e/ato) copper(II) complexes (yields up to 97% and TONs up to 485 after 60 min, and TOFs of up to 1170 h after 10 min reaction) or bis- and tris-pyridyl amino and imino thioether Cu and Fe complexes, with a maximum yield of acetophenone of 99% after 30 min at 80 °C. The maximum TOF of 5220 h (corresponding to 87% yield) was achievedjust after 5 min of reaction time under the low MW power of 10... 

Fernandes RR, Lasri J, da Silva MFCG, da SHvaJAL, da Silva JJR F, Pombeiro AJL. Bis- and tris-pyridyl amino and imino thioether Cu and Fe complexes. Thermal and microwave-assisted peroxidative oxidations of 1-phenylethanol and cyclohexane in the presence of various N-based additives. J Mol Catal A Chem. 2011 351 100-111. 

In another creative application of this strategy, chemists at Pfizer developed a parallel friendly approach to amidines which are again typically available with very limited diversity. Key to success of this method was the utilisation of a mild two-step process that involved reaction of the nitrile class of monomers (which are again available in much larger number than amidines and can also be derived from acids in situ) with N-acetyl cysteine followed by reaetion of the intermediate imino-thioether with ammonia in methanoP (Scheme 18.14). 

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