Thanks to their lack of polarity, the exocyclic double bonds of 4-alkylidenecyclopentenones 4 are selectively epoxidized by MCPBA to give spiroepoxycyclopentenones 7, which feature the nonclassical 1-oxaspiro[2.4]hept-6-en-5-one framework. Under acidic conditions, compounds 7 undergo ring-opening to afford 4-hydroxy-4-(1-hydroxyalkyl)cyclopentenones 10.

The carbonyldicobalt-mediated alkyne/allene/CO cocyclization gives 4-alkylidenecyclopentenones as the major [2+2+1] cycloadducts. The regio- and stereoselectivities depend mainly on the substitution pattern of both the alkyne and the allenic moieties, which can be rationalized using the Magnus mechanism. However, contrary to this model, and in agreement with more recent mechanistic studies, our results provide evidence that both initial pseudo-equatorial and pseudo-axial coordination modes of the allenic hydrocarbons onto one of the cobalt atoms of the primary alkyne dicobalt complex are involved. DFT calculations supporting both these coordination modes are given.

The resolution of α-alkyl-α-hydroxymethylcyclopentanones 1 and cyclohexanones 3 has been efficiently achieved by using lipase-catalyzed transesterification reactions with vinyl acetate as the acylating agent. The enantiomeric selectivities were dependent on both the ring size of the cycloalkanone and the bulk of the carbon group located at the stereogenic quaternary center. The resolved α-alkyl-α-hydroxymethylcyclopentanones 1 were used as enantiopure (or enantioenriched) precursors for the synthesis of the optically active pseudoiridolactones 6–7.

AbstractA comprehensive study of the reaction of in situ generated dicobalthexacarbonyl complexes of disubstituted alkynes, terminal alkynes, or acetylene with a variety of mono‐ and disubstituted allenes is presented yielding mainly the title cyclopentenones.

The base-mediated cyclocondensation reactions of 3-(ethoxycarbonylmethyleile)- and 3-(cyanomethylene)cyclohexenones with ethoxymethylenemalonate derivatives lead to two functionalized alpha-tetralones with selectivities which depend oil the stoichiometric ratio or the reactants. alpha-Tetralones are selectively obtained when excess Michael acceptor is Used.

Biginelli-Atwal condensations of (+)-pulegone with (thio)ureas and guanidine afford hexahydroquinazoline-2(1H)-ones (-thiones) and/or 2-amino-1,3-thiazines with selectivities that depend on both the (thio)ureas and the experimental conditions. Carboannelation of these heterocyclic adducts with diethyl ethoxymethylenemalonate leads to uncommon pyrimidoquinazoline and pyrimidobenzothiazine systems.

The Pauson-Khand-like carbonylative cocyclizations of alkynes with cyclopropylallene and with 1,3-dicyclopropylallene occur regioselectivety and lead to 4-(cyclopropylmethylene)cyclopentenones (43-59% for six examples).

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Bicyclic δ-lactones with a carbon group at the bicyclic junction C-7a, designed as pseudoiridolactones, were synthesized from α-alkyl-α-hydroxymethylcyclopentanones via an intramolecular Horner–Wadsworth–Emmons reaction.

The exocyclic double bonds of 4-alkylidenecyclopentenones are selectively epoxidized by MCPBA to give epoxy-cyclo-pentenones, which under acidic conditions undergo ring-opening to furnish diols.

4-Alkylidenecyclopentenones were shown to be prone to polyalkylation because of their very easy enolization. They were selectively monoalkylated through the organozinc aided alkylation of their new fulvene-type enolates.

Bicyclic δ-lactones, iridolactones analogs with an alkyl group at the bicyclic junction, are obtained from α-alkyl-α-hydroxymethylcyclopentanones via an intramolecular Horner–Wadsworth–Emmons reaction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The amine oxide-promoted Pauson–Khand cycloaddition of 7-oxanorbornene and norbornadiene derivatives affords easily oxa-bridged bicyclic cyclopentenones with satisfactory 60–80% yields.

The regioselectivity of the cobalt-mediated cocyclisation of alkynes with allenic hydrocarbons leading to 4- and 5-alkylidenecyclopentenones was shown to depend on the substitution pattern of both the acetylenic and allenic components. An initial pseudoaxial coordination of the allenic hydrocarbon may account for the formation of the 5-alkylidenecyclopentenone from acetylene.

α-Substituted statines derivatives were synthesized via the zinc-mediated allylation of N,N-dibenzyl α-aminoaldehydes followed by ozonolysis of the intermediate homoallylic alcohols.