Herstellung von 1, 3‐Diketonen und von Nitro‐diketonen durch (1:1)‐Acylierungen von Lithiumenolaten mit Acylchloriden

Abstract

Slow addition of precooled solutions of lithium enolates in THF (Fig. 1 ) to solutions of equimolar amounts of acyl chlorides in the same solvent at temperatures between -80 and -100" furnishes 1,3-diketones in acceptable to good yields (Tables 1-3). Even 3-nitropropionyl and 4-nitrobutyryl chloride can be employed for the (1 : 1)-acylation of enolates to give the synthetically useful 5and 6-nitro-l,3diketones 13 and 25, respectively. The scope and the limitations of this method of preparing 1,3-diketones are given and are compared with alternative methods. 1. Einleitung. -Zur Acylierung von Ketonen zu 1.3-Dicarhonylverbindungen sind prinzipiell viele Methoden bekannt [l] [2]. Beim Einsatz von Enolaten liegt die Schwierigkeit vor allem darin, aus einem Mol-Aquivalent Keton-enolat und einem Mol-Aquivalent Acylierungsmittel moglichst hohe Ausbeuten an 1,3-Diketonen zu erzielen, also eine Deprotonierung des Diketons durch das Ausgangsenolat zu vermeiden. Um Enolate ganz zu umgehen, wurden an deren Stelle 2.B. Silylenolather [3], metallierte Hydrazone [4] oder Enamine [5] [6] verwendet. Die erste Methode ist beziiglich der Acylchloride nur bedingt anwendbar [3] (es wurden lediglich Di-und Trichloracetylchlorid umgesetzt), und die oftmals energischen Hydrolysebedingungen in der Folge der beiden letztgenannten Verfahren bedeuten eine Beschrankung beziiglich der Anwesenheit weiterer funktioneller Gruppen.Der ambidente Charakter und die gegeniiber den zu bildenden 1,3-Diketonen hohe Basizitat von Enolaten lassen Schwierigkeiten wie 0-Acylierung, Umprotonierung, doppelte Acylierung und damit nicht zuletzt niedrige Ausbeuten an

The World of β‐ and γ‐Peptides Comprised of Homologated Proteinogenic Amino Acids and Other Components

“…Besides the 14-membered rings, 10-and 12-membered rings are also to be found in the b 3 -peptide, which, according to NMR analysis, exists in the 3 14 -helical form, and together with 10-and 12-membered rings of the 10/12-helix found in the b 2 /b 3 -peptide by NMR investigation, there are also 14-membered rings to be discovered. The dominance of 10-membered rings in the b 2 /b 3 -peptide is striking; it was later established by MD simulation 43 ) that it also exists to a not unappreciable degree as a turn, [274] which also contains a 10-membered ring! (see Fig.…”

“…39, bottom. In the data set for the b 2 /b 3 -hexapeptide with a 10/ 12-helical NMR structure, a few percent of the 3 14 -helix [216] [217] and of the turn [274] structures are also found, while in that for the b-hexapeptide turn a so-called −cluster× of 10/12-helical conformers is seen 43 ). The experimentally determined NMR solution structure may be present in the conformational mixture only to the extent of 20 ± 30%, and the NMR method may completely fail to −see× the other conformers.…”

“…2, of what happens when one or two CH 2 groups are introduced into each amino acid in a peptide, we shall restrict the discussion in the following Chapt. 6 and 7 ± as stated in this article×s title ± to peptides made out of homologated proteinogenic amino acids, studied until recently exclusively by our group 42 ) 43 ).…”

“…Meanwhile, several review articles in which b-peptide chemistry is described either exclusively or in a greater or lesser degree of detail have also appeared [7] [17] [253 ± 272]. 43 ) See [273] [274] and the earlier publications by van Gunsteren×s group cited therein. 44 ) The strict standards defined by P. Fuchs for synthetic efficiency (IQ and EQ coefficients) could also not be claimed [275].…”

Tritylketone und Tritylenone. Beiträge zur sterisch erzwungenen Michael‐Addition und zur diastereoselektiven Aldol‐Addition

“…4, products &20, 10 examples); the OH-group of the aldols 10 must be EE-, MOM-or MEM-protected (Scheme 8) before this C,C-bond cleavage can be conveyed. Some of the cleavage products are used for the chemical correlation of the aldol configuration and for the demonstration of the synthetic value of the presented method (see [21][22][23][24][25][26][27][28][29] …”