Allenic Esters Research Articles

Electrophilic fragmentation-cyclization of various allenic esters

Electrophilic fragmentation-cyclization of various allenic esters

Transfert de l'ethoxycarbonylcarbene sur les alcynes substitues en α par un groupe partant

Synthesis of ethyl cyclopropenecarboxylates with a leaving group on the position α to the double bond has been realised by photolytic or thermocatalytic decomposition of ethyl diazoacetate with acetylenic substrates. With these adducts allenic, a etylenic or dienic esters are obtained. In the case of photolytic transfer, the proposed intermediate agent is ethoxycarbonyl carbene. If the transfer is thermocatalytic, addition of ethyldiazoacetate to the acetylenic substrate giving pyrazolenines, and decomposition giving a carbenoid, are competitive reactions. Thermal or thermocatalytic isomerisation of ethyl halogens cyclopropene-carboxylates is also studied. When exocyclic migration of the cyclopropenic double bond occurs, a stereospecific migration of halogen is observed.

Pheromone synthesis. 4. A synthesis of (.+-.)-methyl n-tetradeca-trans-2,4,5-trienoate, an allenic ester produced by the male dried bean beetle Acanthoscelides obtectus (Say)

Pheromone synthesis. 4. A synthesis of (.+-.)-methyl n-tetradeca-trans-2,4,5-trienoate, an allenic ester produced by the male dried bean beetle Acanthoscelides obtectus (Say)

Absolute configuration of allenes, conversion of molecular dissymmetry into centrodissymmetry by heterogeneous catalytic hydrogenation

Palladium-catalysed hydrogenation of 4-methylhexa-2,3-dienoic acid and its methyl ester has been studied, by product analysis, over the complete range of hydrogen absorption. 4-Methyl[1-14C]hex-cis-2-enoic and 4-methyl[1-14C]hex-3-enoic acid and methyl ester have been employed in co-hydrogenations with the allene, which show that the substantial amount of 4-methylhex-trans-2-enoic acid (or ester) formed in the first stage arises neither directly from the allene, nor by isomerisation of the 3-enoic acid, but by stereomutation of 4-methylhex-cis-2-enoic acid on the catalyst. The conversion of molecular dissymmetry into centrodissymmetry by catalytic hydrogenation can therefore be used to determine the absolute configuration of allenes.(–)-Methyl 4-methylhexa-2,3-dienoate gave (–)-(R)-methyl 4-methylhexanoate on catalytic semi- and full-hydrogenation and, from analysis of steric effects in the transition state for adsorption, the (–)-allene ester has the R-configuration. Semihydrogenation of the (+)-allenic acid, followed by esterification, gave methyl (+)-4-methylhex-2-enoate, oxidised and esterified to (+)-(S)-methyl 2-methylbutyrate: this provides a variant of the method. The assumption of cis-addition of hydrogen from the catalyst surface is formally proved by hydrogenation of (+)-methyl 4-phenyl-penta-2,3-dienoate of established S-configuration.

Heterogeneous catalytic hydrogenation of allenes over supported palladium: selectivity, stereoselectivity, and regioselectivity

The palladium-catalysed hydrogenation of twelve allenes has been studied, from the point of view of product composition, over the complete range (0–2 mol. equiv.) of hydrogen absorption. Selectivity, stereoselectivity, and regioselectivity have been estimated with special reference to the semihydrogenation point. The relative haptophilicities of the four possible approaches of suitably substituted allenes to the catalyst surface show that steric effects play a major role in determining which orientations shall lead to product formation. In the case of conjugated allene esters and acids however, parallel orientation of the ester and acid groups is unexpectedly disfavoured: this may imply repulsive electronic contributions.

Preliminary biological studies on the pheromone produced by male Acanthoscelides obtectus (Say) (Coleoptera, Bruchidae)

Virgin female Acanthoscelides obtectus (Say) placed in a closed 12·5 cm Petri dish were attracted to a caged male by a pheromone which could be extracted with hexane and was extremely stable in solution. Surfaces which had been exposed to males attracted virgin females. The male did not respond to a caged female although on coming into contact with a free female he usually pursued her and attempted to mate. Mating lasted about 10 min after which females usually resisted any further attempts made by males during the 8 hr period of observation. After mating or removal of antennae females were not attracted by caged males and remained unresponsive for the rest of their lives. Virgin females given the choice between male pheromone and the smell of beans chose the former. Male extract presented on a variety of substrates usually attracted virgin females but a few failures occurred. When extract was run on a thin layer chromatogram and presented to virgin females they were only attracted to the region carrying the allenic ester (−)-methyl n-tetradeca-trans-2,4,5-trienoate, and extract without it (removed using chromatographic techniques) proved inactive. The allenic ester therefore appears to be at least closely related to the pheromone.

Allenes. Part XXVIII. Synthesis of antibiotic lactols and an allenic ester by Claisen rearrangement of prop-2-ynyl vinyl ethers

Naturally occurring 4-hydroxy-2-vinylbut-2-en-4-olide (V), an allenic analogue [4-hydroxy-3,3-dimethyl-2-vinylidenebutan-4-olide (VII)], and the corresponding aldehyde ester [ethyl 2-(1-formyl-1-methylethyl)buta-2,3-dienoate (VIII)] have been synthesised by a Claisen-type sigmatropic rearrangement of 3-carboxyprop-2-ynyl vinyl ethers.

Thallium in Organic Synthesis. XXXVI.New synthesis of allenic esters

Thallium in Organic Synthesis. XXXVI.New synthesis of allenic esters

(-) methyl n-tetradeca-trans-2,4,5-trienoate, an allenic ester produced by the male dried bean beetle, Acanthoscelides obtectus (Say).

A substance produced by the male Dried Bean beetle has been characterised as methyl n-tetradeca-trans-2,4,5-trienoate. This is thought to be the first example of an allenic compound occurring in the animal kingdom. It is presumed to be a sex attractant.

Cycloadditions. Part III. Steric effects in the addition of 2-diazopropane to conjugated allenic esters and nitriles

Esters of buta-2-,3-dienoic acid and its methyl-substituted analogues react with 2-diazopropane at more electrophilic (αβ) double-bond, but the orientation of addition is dependent on the degree of substitution at the γ-carbon atom. Allenes monosubstituted or unsubstituted at the γ-position give 4-alkylidene-1-pyrazolines (i.e. the electronically preferred adducts). The initial adduct from methyl buta-2,3-dienoate isomerises under the reaction conditions to 3-methoxycarbonyl-5,5-dimethyl-4-methylene-2-pyrazoline, which reacts readily with a second molecule of 2-diazopropane to give a spiran. The orientation of addition is reversed with γγ-disubstituted allenic esters and nitriles, which give solely 3-isopropylidene-1-pyrazolines. The reversals are attributed to a highly unfavourable ‘wedging’ interaction in the transition states for normal addition to the γγ-dimethylallenes. The orientation in several other allene-diazoalkane cycloadditions is discussed.The 3-isopropylidene-1-pyrazolines give good yields of isopropylidenecyclopropanes on photolysis.