Josep M. Moretó

Dimethyldioxirane in organometallic chemistry. II: An improved procedure for the oxidative decomplexation of fischer carbene complexes

Abstract Treatment of Fischer carbene complexes 1 with dimethyldioxirane affords good conversion yields of the corresponding oxo derivatives 2 , in a clean and highly chemoselective reaction.

Stereoselective synthesis of bicyclo[3.3.0]oct-1-en-3-one derivatives

Abstract Intramolecular carbonylative cyclization of either E or Z -9-methoxy-2-nonen-7-ynyl bromide promoted by Ni(CO) 4 afforded the same isomer of 4-(methoxycarbonylmethyl)-2-(methoxymethyl)bicyclo [3.3.0]oct-1-en-3-one in 43–50% yields with a relative trans -configuration of H-4 and H-5 protons.

A total synthesis of methylenomycin B

Abstract A new synthesis of methylenomycin B (1) has been accomplished in four steps starting with a NI(CO) 4 promoted cyclocondensation reaction of allyl chloride and 2-butyn-1-ol in MeOH, followed by hydrogenolysis of the resulting mixture to 2,3-dimethyl-5-methyl-oxycarbonylmethyl-2-cyclopentenone (3), which by hydrolysis and oxidative decarboxylation yielded 1.

A two step procedure as improved alternative to the cyclocarbonylation of allyl halides and acetylene derivatives mediated by Ni(CO)4

Abstract The addition of allyl halides to acetylenic derivatives catalyzed by Pd(II) complexes, such as bis-acetonitrile palladium(II) bromide, followed by cyclocarbonylation of the resulting cis adducts with Ni(CO) 4 in CH 3 CN containing precise amounts of CH 3 OH and Et 3 N is a better procedure than the direct cyclocarbonylation of these substrates mediated by Ni(CO) 4 for preparation of cyclopentenones, specially for monosubstituted acetylenes or weakly polarized disubstituted acetylenes.

Reactions of silyl enol ethers with [ethoxy(phenylethynyl)carbene]chromium and -tungsten complexes

Abstract The reaction of pentacarbonyl[ethoxy(phenylethynyl)carbene]chromium with silyl enol ethers yields cyclobutenylcarbene complexes in moderate-to-good yield by a process that involves a Michael-type addition of the nucleophilic enol ether to the Fischer carbene complex. An ene-type product and two pyranylidene chromium complexes were also obtained in these reactions. A pyranylidene complex was also obtained in the reaction of the related tungsten complex with ( Z )-1,3-bis(trimethylsilyloxy)-1-ethoxy-1,3-butadiene.

An efficient synthesis of 3,4-dioxocyclobutenecarboxylate derivatives

Abstract Alkynylalkoxycarbene metal complexes react readily with tetraalkoxyethylenes to give the corresponding [2 + 2] cycloadducts in high yields. From these adducts the title compounds were obtained by DMSO oxidation and final hydrolysis of the acetal groups.

Trapping of a carbanionic intermediate in the reaction of alkynylalkoxy carbene metal (Cr) complexes and ethyl diethoxyacrylate

Abstract A new bis(carbene) metal complex was isolated and fully characterized in the reaction of alkynylalkoxy carbene metal complexes and ethyl diethoxyacrylate. This complex represents the trapping of a carbanionic intermediate in the above mentioned reaction.

REACTION OF ETHYL 3,3-DIETHOXYACRYLATE WITH FISCHER ALKOXYALKYNYL TRANSITION METAL CARBENE COMPLEXES

Abstract The title reaction afforded various amounts of differently substituted pentacarbonyl pyranylidene complexes, depending on factors such as the metal, substitution at the alkynyl moiety and relative ratio of the reagents employed. The results obtained are explained by a cycloaddition-ring-opening mechanism giving intermediates that can further cyclize to pyranylidene derivatives. The importance of the dialkoxy and ester groups in promoting this cyclization was studied by replacing ethyl 3,3-diethoxyacrylate by model compounds, such as 4,4-dimethoxybut-3-en-2-one and 2-[(methoxycarbonyl)methylidene]-1,3-dioxolane.

Change of the Reaction Pattern by Methodological Variations in a Multicomponent Assembly Promoted by Ni Complexes

The pi-allylnickel complex formed by the addition of trimethylsilyl chloride (TMSCl) to a mixture of [Ni-(cod)2] (cod = 1,5-cyclooctadiene) and a vinyl ketone (Mackenzie complex) carbometalates an acetylene in a completely regioselective manner resulting in the formation of the corresponding vinyl nickel species. This intermediate is capable of controlled quenching in a variety of ways to give different types of compounds: under a CO atmosphere, an acylnickel species is formed that ensues from the carbometalation of the enol ether double bond to form cyclo-pentenone derivatives. Alternatively, if acetylene is present in excess and CO is absent, another acetylene moiety will replace the CO and cyclohexadienes will result instead. Finally, if only an excess of the vinyl ketone is used, the product from a slow double addition of the vinyl ketone across the triple bond is formed. The regioselectivities obtained by the present method are different from those obtained by the involvement of nickel acyclopentadienes as intermediates when the order of addition is reversed.

Ni(COD)2: an efficient promoter in the construction of 5-cyclopent-2-enone derivatives from allyl halides, alkynes and carbon monoxide

Abstract Cyclopentenone derivatives are obtained from alkynes, allyl halides and carbon monoxide in a single synthetic operation by the use of Ni(COD) 2 with minimal formation (if any) of Ni(CO) 4 . The initial formation of a π-allyl nickel complex, first intermediate in the so far postulated mechanism, is a valid pathway to the three component cycloaddition. However, care should be taken to minimize the side reactions in the process, the extension of which depends on the nature of both the alkyne and the allyl derivatives. Reliable monitoring of the components throughout the process results in good yields of the cycloadducts.