Massenspektrometrische Untersuchung von Amiden. VIII—Vinyloge α-Spaltung und Nachbargruppenbeteiligung bei der Fragmentierung von Piperididen α,β-ungesättigter Carbonsäuren

The electron-impact-induced fragmentation of piperidides from β-substituted α, β-unsaturated carboxylic acids proceeds preferentially via 4-membered cyclic transition states. The development of a 6-membered ring, which is typical for α,β-unsaturated esters, occurs only to a minor extent. The mechanism of the reaction is best rationalised by the assumption of a vinylogous α-cleavage and a simultaneous neighbouring group participation of the amide function     

Über einen neuartigen synthetischen Zugang zu β,γ-ungesättigten α-Aminocarbonsäuren

A New Synthetic Route to β,α-Unsaturated α-Amino Acids A versatile new synthetic pathway for the preparation of βγ-unsaturated α-amino acids ( 1 ) is presented. Cu(I)-catalyzed addition of ethyl isocyanoacetate ( 2 ) to α-chloro carbonyl compounds ( 3 ) gives 5-chloroalkyl-2-oxazolin-4-carboxylates ( 4 ) in high yields. A reductive elimination on 4 by means of zinc yields the N-formyl derivatives of βγ-unsaturated α-amino carboxylates ( 5 ), which on acid hydrolysis lead to the free amino acids 1 . The five different βγ-dehydro-α-amono acids 1b-1f have been prepared by this method.     

Synthesen von 2-Pyronen aus α, β-ungesättigten Säurechloriden und tertiären Aminen

A new synthesis of 2-pyrones has been developed. Two molecules of α, β-unsaturated acid chlorides ( 8 , 12 and 18 ) condense, with loss of two molecules hydrogen chloride, to pairs of substituted 2-pyrones ( 9 and 10 , 13 and 14 , 19 and 20 ) when treated with triethyl amine in chloroform or methylene chloride at room temperature. In the case of 18 , two additional products were obtained, namely the resorcinol derivative 21 and traces of the 1, 3-cyclobutanedione derivative 22 . Under the same conditions the α, β-unsaturated acid chlorides 8 , 15 , 18 and 41 were condensed with trichloroacetyl chloride to give 6-trichloromethyl-2-pyrones ( 42 , 43 , 44 and 46 ). These 2-pyrones are valuable intermediates for the synthesis of 6-carboxy-2-pyrones and 6-methyl-2-pyrones. A methyl group in β-position of the α, β-unsaturated acid chloride appears to be essential for the described condensations, for the acid chlorides 16 and 17 did not yield defined products and the acid chloride 40 reacted with trichloroacetyl chloride in a very low yield. It is considered that the described reactions proceed via the 1, 4-addition of an acid chloride to a vinyl ketene or through the acylation of an intermediate anion by an acyl derivative as outlined in reaction scheme 1. The structures of the 2-pyrones were confirmed by their spectroscopic properties, summarized in table 3, and by some of their chemical transformations.     

Die Acylierung von Acetylenen mit β, γ-ungesättigten Säurechloriden. Eine neue Synthese von 5-Cyclopentenonen

The Acylation of Acetylenes with β,γ-Unsaturated Acid Chlorides, A New Synthesis of 5-Substituted 2-Cyclopentenones The acylation of acetylenes with α,α-disubstituted, β,γ-unsaturated acid chlorides under Friedel-Crafts-type conditions leads to 5-substituted 2-cyclopentenones. Phenols are formed with β,γ-unsaturated acid chlorides bearing at least one α-H-atom. These transformations are explained by the intramolecular cyclization of the initially formed vinyl cation, which, in the cases of α,α-disubstituted acid chlorides, is followed by ring contraction. The reaction leading to 2-cyclopentenones is applied to the synthesis of some spiro[4.4]nona- and spiro[4.5]deca-2,6-dienones.     

Eine einfache und flexible Synthese von Pyrrolen aus α,β-ungesättigten Sulfonen

A Simple and Flexible Synthesis of Pyrroles from α , β -Unsaturated Sulfones: The addition of alkyl isocyanoacetates and isocyanoacetonitrile to α,β-unsaturated sulfones affords a convenient and broad access to pyrroles with unusual substitution patterns (see Scheme 2). The α,β-unsaturated sulfones required as starting materials are easily obtained from different olefines.