Oxazoles Mannich reaction

H,3H- Pyrrolo[l, 2-c]oxazole-l, 3-dione, 5,6,7,8-tetrahydro-IR spectra, 6, 978 [2.2](2,5)Pyrrolophane, N-aryl-rearrangements, 4, 209 Pyrrolophanes natural products, 7, 764 synthesis, 7, 771 Pyrrolophanes, N-aryl-synthesis, 7, 774 (2,4)Pyrrolophanes synthesis, 7, 771 Pyrrolo[3,4-c]pyran-4-ones synthesis, 4, 288 Pyrrolopyrans synthesis, 4, 525, 526 Pyrrolopyrazines synthesis, 4, 526 Pyrrolo[l, 2-a]pyrazines synthesis, 4, 516 Pyrrolo[2,3-6]pyrazines Mannich reaction, 4, 504 Vilsmeier reaction, 4, 505 Pyrrolo[3,4-c]pyrazole, 1,3a,6,6a-tetrahydro-structure, 6, 976 synthesis, 6, 1019 Pyrrolopyrazoles synthesis, 5, 164 Pyrrolo[l,2-6]pyrazoles synthesis, 6, 1002, 1006 Pyrrolo[3,4-c]pyrazoles reactions, 6, 1034 synthesis, 6, 989, 1043 Pyrrolo[3,4-c]pyrazolones synthesis, 6, 989 Pyrfolopyridazines synthesis, 4, 517 Pyrrolo[l, 2-6]pyridazines synthesis, 4, 297 6/7-Pyrrolo[2,3-d]pyridazines synthesis, 4, 291 2/f-Pyrrolo[3,4-d]pyridazines synthesis, 4, 291 6/7-Pyrrolo[3,4-d]pyridazines synthesis, 4, 291... 

In a number of multicomponent condensation reactions, TMSCl has also been utilized to inprove the yield or efficacy of the desired product, or is directly incorporated into the final molecules. Examples include the s)fnthesis of Al-aryl-3-arylamino acids from a three-component reaction of phenols, glyoxylates, and anilines, preparation of 2,4,5-trisuhstituted oxazoles, or 4-cyanooxazoles, and the three-component Biginelli reaction (eq 92) and Biginelli-like Mannich reaction of carhamates, aldehydes, and ketones. 

A C=C triple bond of 1,3-diyne 149 was cleaved with 2-aminophenol in the presence of a ruthenium catalyst (Scheme 7.52) [71]. Initially, a ruthenium-catalyzed hydroamination takes place to give alkynyl imine 150. Conjugate addition of 2-aminophenol follows, resulting in the formation of the 1,3-diimine 151, which cyclizes to form the oxazoline 152. Subsequent retro-Mannich reaction cleaves the C-C bond to furnish the oxazole 153 and the imine 154. 

A highly diastereo- and enantioselective zinc-catalysed Mannich reaction of imines (508) with 5/f-oxazol-4-ones (514), which leads to the first catalytic asymmetric synthesis of q n-a-allgrl norstatine derivatives (515) has been also described (Scheme 171). ... 

The use of an a-isocyanoacetamide instead of an a-isocyanoacetate is essential in order to obtain oxazoles when the latter compounds are employed, other condensations (Knoevenagel, Mannich), affording imidazolines or amidines, will take place [88]. This reaction has been explored for the preparation of a series of 2-imidazolines employing isocyanoacetates [91]. The reaction worked smoothly to give compounds 105a,b (Scheme 1.36) with the trans isomer prevailing, provided that a racemic isocyanide with an acidic a-proton and a sterically undemanding amine are used. 

These systems are reported as cyclopentaoxazolidines and can be obtained by conventional azeotropic dehydration of aldehydes with amino alcohols <85TL5303> for example, (S)-5-Hydroxymethyl-2-pyrrolidinone (236) was condensed with benzaldehyde to obtain the corresponding chiral 5-oxo-2-phenylperhydropyrrolo[l,2-c]oxazole (237) in excellent yield <86JOC3140>. Similar treatment of enantiomerically pure amino ketone (238) with paraformaldehyde or formalin under a variety of Mannich conditions yielded (239) <84ja5360>. These reactions are shown in Scheme 41. 

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