Methylene carbonyl

Mannich Reaction - a,p-unsaturated carbonyls (a-methylene carbonyls)... 

PFITZINGER Quinoline synthesis QumoHne-4-cartx)xyHc acids from isatin and a-methylene carbonyl compounds. 

The Pfitzinger reaction entails the synthesis of quinoline-4-carboxylic acids 2 via condensation of isatic acids formed from isatins 1 and a-methylene carbonyl compounds in the presence of strong aqueous bases. Subsequent decarboxylation can afford the corresponding quinolines. " ... 

Quinolines 3 can be obtained from reaction of orr/zo-aminobenzaldehydes or o-aminoarylketones 1 with a-methylene carbonyl compounds.Various modified procedures are known a related reaction is the Skraup quinoline synthesis. 

The aminoketone 1, required as starting material, can be obtained by a Neber rearrangement from a A -tosylhydrazone. Another route to a-aminoketones starts with the nitrosation of an a-methylene carbonyl compound—often in situ—to give the more stable tautomeric oxime 7, which is then reduced in a subsequent step to yield 1 ... 

The dialkylaminomethyl ketones formed in the Mannich reaction are useful synthetic intermediates.184 Thermal elimination of the amines or the derived quaternary salts provides a-methylene carbonyl compounds. 

The Pfitzinger reaction of isatins with a-methylene carbonyl compounds is widely used for the synthesis of substituted quinoline-4-carboxylic acids. Ivachtchenko and colleagues have recently reported on the Pfitzinger reaction in a series of 5-sulfa-moylisatins (Scheme 6.239) [422]. Treatment of 5-sulfamoylisatins with diethyl mal-... 

Condensation of o-aminobenzaldehydes with a-methylene carbonyl componnds... 

Pyrrole synthesis from at-dicarbonyl compounds.15 A new approach to N-benzyl-pyrroles is formulated for biacetyl as starting material (equation I). The method is also suitable for annelation of a pyrrole group to an a-methylene carbonyl compound. 

The Gewald Reaction is a synthesis of 2-aminothiophenes via a multi-component condensation between sulfur, an a-methylene carbonyl compound and an a-cyanoester. 

Asymmetric Baylis-Hillman reactions using sugar acrylates have been reported to proceed with moderate diastereoselectivity (5-40% ee) [23]. The reaction of camphor-based chiral acryloylhydrazides with aldehydes in the presence of DABCO afforded /1-hydroxy-a-methylene carbonyl derivatives in 68-92% yield with high diastereoselectivity (up to 98% de) [24]. Both diastereomers could be selectively obtained simply by changing the solvent. 

Unlike DNA and RNA, which have backbones of repeating sugar-phosphate units, the PNA molecule is built upon a pseudo-peptide backbone of N-(2-aminoethyglycine) units linked by peptide bonds, to which purine and pyrimidine bases (the specific base-pairing units of nucleic acids) are linked via methylene carbonyl bonds. 

The Gewald reaction can be conveniently performed via a multicomponent condensation between sulfur, an -methylene carbonyl compound, and an -cyanoester. The use of ionic liquids as solvents <2004SC3801>, or performing this condensation under microwave irradiation without solvent (Scheme 84) <2005SC1351>, leads to generally better yields of 2-aminothiophenes . 

PFITZINGER Quinoline synthesis ai ioline-4-cart xylic acids from isatin and o-methylene carbonyl compounds. 

Abdou, W.M., and El Khoshnieh, Y.O., Synthesis of fused thioxo-pyran systems from a-methylene carbonyl compounds and bz.vmclhylcnc-l, 3-dilhictanc, Synth. Commun., 29, 2657, 1999. 

The most direct synthesis of 1,4-dihydropyridines (7b) utilizes a procedure with either <5 + 1>, <3 + 2+1), or <2 + 1 + 2 + (1)> fragment combination. The latter represents the widely used classical Hantzsch s synthesis, which combines two molecules of an active a-methylenic carbonyl compound, an aldehyde, and an ammonia source (Scheme 3). 

The simplest polycycles stem from two triply-bridged points. These systems are exemplified by Trost et al. s 4,8-dihydrodibenzo[oi,g7z]pentalene (69) [87, 88], a precursor for a purturbed [12]annulene dianion, and Mislow et al. s double-bridged biphenyl derivatives (generally shown as 70) [89], where X is methylene, carbonyl, or various heteroatoms. Other longer bridged biphenyls include the triple-bridged cyclophanes 71 made by Hubert and Dale [90], their unsym-metrical relatives by Cram and Reeves [91], and the recent polyalkynyl cyclo-phane (72) made by Rubin et al. [92], a proposed fullerene precursor. 

---