2-Cyclopentanone carboxylic acid

Cyclopentanones from carboxylic acids by intramolecular acylation of alkyl-silanes... 

Limited progress has been achieved in the enantioselective hydrogenation of a,/ -unsaturated carboxylic acid esters, amides, lactones, and ketones (Scheme 26.10). The Ru-BINAP system is efficient for the hydrogenation of 2-methy-lene-y-butyrolactone, and 2-methylene-cyclopentanone [98]. With a dicationic (S)-di-t-Bu-MeOBIPHEP-Ru complex under a high hydrogen pressure, 3-ethoxy pyr-rolidinone could be hydrogenated in isopropanol to give (R)-4-ethoxy-y-lactam in 98% ee [39]. 

CYCLOPENTANONES FROM CARBOXYLIC ACIDS VIA INTRAMOLECULAR ACYLATION OF ALKYLSILANES Z-METHYL-2-VINYLCYCLOPENTANOHE (Cyclopentanone, 2-ethenyl-2-methyl-)... 

This is a general method of preparing enamines from a secondary aliphatic amine and cyclohexanone or cyclopentanone. Acylation of such enamines is the first step in a general procedure for increasing the chain length of a carboxylic acid by 5 or 6 carbon atoms and of a dicarboxylic acid by 10 or 12 carbon atoms.6 Alkylation of enamines of cyclohexanones by alkyl halides 7 or electrophilic olefins,8 followed by hydrolysis, is a good route to a-monoalkyl cyclohexanones. 

The methyl ester has also been obtained by esterification of cyclopentanecarboxylic acid.8 The acid, in turn, has been prepared by the Favorskii rearrangement,6 7 9-11 by the reaction of cyclopentyl Grignard reagent with carbon dioxide,12 by the carbonylation of cyclopentyl alcohol with nickel carbonyl13 or with formic acid in the presence of sulfuric acid,14 and by the hydrogenation of cyclopentene-1-carboxylic acid prepared from ethyl cyclopentanone-2-carboxylate 15 or from cyclopentanone cyanohydrin.16... 

Oxobutyl)cyclopentanone-2-carboxylic Acid Ethyl Ester. 

Several examples have been described on Lewis acid and base catalyzed Michael additions. Cyclopentanone-2-carboxylic acid ethylester was added at room temperature to methyl vinyl ketone using 2 mol% FeCl3 -6 H20 as catalyst yielding > 90% of the addition product (Scheme 11) [31]. Cerium(III) chloride in the presence of sodium iodide [32] and trifluoro-methanesulfonic acid have been used as catalysts as well [33]. 

Cyclopentanone 1 carboxylic acid lenacil Cyclopentylamine pencycuron... 

Dimethyl 5 methyl carboxylic acid cyclopentanone metconazole Dimethyl chloro methyl acetyl chloride dimethazone... 

R Cyclopentanones from Carboxylic Acids via Intramolecular Acylation of Alkyl silanes 2-Methyl-2-vinyl cyclopentanone... 

A different approach was adopted in the synthesis by Justoni and Pessina (111). The Japp-Klingemann reaction of p-benzyloxyphenyl-hydrazine with cyclopentanone carboxylic ester gave the p-benzyloxy-phenylhydrazone of a-ketoadipic acid (XIV) Fischer cyclization of the corresponding dimethyl ester then yielded 5-benzyloxyindole-2-car-boxylic-3-jS-propionic acid (XV). Decarboxylation of XV followed by Curtius degradation and debenzylation eventually afforded 5-hydroxy-tryptamine. 

Pyrethrum (Chrysanthemum) dnerarifolium (Asteraceae) namely cinerin I (CMC cineralone ester), cinerin II (CDC monomethyl ester cinerolone ester), pyrethrin I (CMC pyrethrolone ester) and pyrethrin II (CDC monomethyl ester pyrethrolone ester). The chrysanthemum carboxylic acids are cyclopropane-based monoterpenes and cineralone and pyrethrolone are cyclopentanone monoterpene alcohols. The pyrethrins (and their insecticidal synthetic derivatives) are toxic to insects through keeping cell membrane voltage-gated Na+ channels open and thus impairing neurotransmission. 

Intramolecular acylation of alkylsilanes. Cyclopentanones can be prepared by ring closure of 5-(trimethylsilyl)alkanoyl chlorides mediated by AlCl,. The starting materials are readily available from alkylation of the dianion of a carboxylic acid with a 3-(trimethylsilyl)alkyl bromide or iodide (equation 1). 

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