Diene

Summary

In organic chemistry, a diene (ˈdaɪiːn ); also diolefin, daɪˈoʊləfᵻn ) or alkadiene) is a covalent compound that contains two double bonds, usually among carbon atoms. They thus contain two alkene units, with the standard prefix di of systematic nomenclature. As a subunit of more complex molecules, dienes occur in naturally occurring and synthetic chemicals and are used in organic synthesis. Conjugated dienes are widely used as monomers in the polymer industry. Polyunsaturated fats are of interest to nutrition. Classes Dienes can be divided into three classes, depending on the relative location of the double bonds: #Cumulated dienes have the double bonds sharing a common atom. The result is more specifically called an allene. #Conjugated dienes have conjugated double bonds separated by one single bond. Conjugated dienes are more stable than other dienes because of resonance. #Unconjugated dienes have the double bonds separated by two or more sing

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New access to long-chain polyketides and spiroketals by umpolung of electron rich dienes with sulfur dioxide

Freddy Fonquerne

Natural polyketides show important biological activity. The inherent stereochemical complexity present in this class of molecules has captured the imagination of organic chemists. Their stereocontrolled, asymmetric total synthesis is a permanent and stimulating area of research. Previous efforts in our group demonstrated that the Umpolung of electron rich 1,3-dienes with SO2 could represent an efficient synthetic strategy to polyketides. Under appropriate conditions sulfur dioxide reacts with 1,3-dienes in the hetero-Diels-Alder fashion. In the case of 1-alkoxy-1,3-dienes, the 6-alkoxy-3,6-dihydro-1,2-oxatiin-2-oxides (sultines) so-obtained can be ionized in the presence of a Lewis or protic acid. The resulting zwitterionic intermediates can be trapped with enoxysilanes (oxyallylation) to generate the corresponding substituted alkenylsulfinates. Desilylation of the latter under acidic conditions leads to allylsulfinic acid intermediates, which, after retro-ene desulfitation, produce 4-alkoxyhepta-6-en-2-one core, a valuable fragment in polyketide natural product synthesis. This new SO2 cascade reaction, hetero-Diels-Alder addition/oxyallylation/retro-ene desulfitation (Vogel's cascade) has been extended to 1-alkoxy-3-acyloxy-1,3-pentadienes. Their use in this cascade reaction allowed the generation of 1,3-polyols array containing keto and enol ester functions, suitable for further chain elongation. In addition, this work highlights the extension of this methodology to other types of p-nucleophiles. The use of carefully elaborated allylsilanes allowed the preparation in a single operation (one pot double oxyallylation reaction) of long chain polyketides of 13 carbons units. Finally, a new route to the spiroketals A/B and C/D and of Spongistatins is presented in order to demonstrate the utility and the versatility of this approach.

EPFL2005

Total asymmetric synthesis of advanced polyketide fragments of apoptolidinone and rectricticin using new organic chemistry of sulfur dioxide

Cotinica Craita

Under appropriate conditions sulfur dioxide reacts with 1,3-dienes in a hetero-Diels-Alder fashion. In the case of 1-alkoxy-1,3-dienes the 6-alkoxy-3,6-dihydro-1,2-oxathiin-2-oxides (sultines) so-obtained can be ionized in the presence of Lewis or protic acids. The zwitterionic intermediates can be trapped as electrophiles with enoxysilanes (oxyallylation) to generate substituted silyl alkenylsulfinates. The latter can then be reacted with TBAF and an electrophile to generate polyfunctional sulfones (one pot, four component syntheses). Alternatively, desilylation through silicon/palladium transmetallation, in the presence of a catalytic amount of Pd(OAc)2, leads to intermediate allylsulfinic acids, which, after retro-ene desulfitation, produce 4-alkoxyhept-6-en-2-one core, a valuable fragment in polyketide natural product synthesis. The first part of this work described the application of an asymmetric version of this new SO2 reaction cascade, hetero-Diels-Alder addition/oxyallylation/retro-ene desulfitation (Vogel's cascade), using enantiomerically enriched dienes. The synthesis of a variety of β-alkoxy ketones was realized with good α,β-syn selectivity, starting from different enoxysilanes, illustrating the versatility of the method. An iterative Vogel's cascade employing newly obtained fragments provided long-chain polypropionate fragments such as (-)-(4R,5R,6S,9S,10R,2E,11E)-4,6,10-trimethyl-5,9-bis-((1S)-1-phenylethoxy)-trideca-2,11-dien-7-one in a very short and efficient way. The synthetic potential of Vogel's cascade reaction was demonstrated by the short and elegant synthesis of the enantiomerically enriched polypropionate fragment (C16-C28) of apoptolidinone, aglycon of apoptolidin, a highly potent apoptosis inducing agent. In the second part of thesis the one pot polyfunctional sulfone synthesis, developed in our group was successfully combined with the aldol methodology of Paterson to reach an advanced polyketide fragment, a potential intermediate in the total synthesis of Restricticin. Finally, in the last part of this study, we have demonstrated that methallyl silylsulfinates, known as new reagents for alcohol silylation are very precious and efficient reagents for the silylation of phenols and carboxylic acids. Additionally, the chemoselectivity of these reagents on substrates containing different hydroxyl groups was demonstrated.

EPFL2006

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At low temperature and in the presence of an acid catalyst, SO2 adds to 1,3-dienes equilibrating with the corresponding 3,6-dihydro-1,2-oxathiin-2-oxides (sultines). These compounds are unstable above -60 degrees C and equilibrate with the more stable 2,5-dihydrothiophene 1,1-dioxides (sulfolenes). The hetero-Diels-Alder additions of SO2 are suprafacial and follow the Alder endo rule. The sultines derived from 1-oxy-substituted and 1,3-dioxy-disubstituted 1,3-dienes cannot be observed at -100 degrees C but are believed to be formed faster than the corresponding sulfolenes. In the presence of acid catalysts, the 6-oxy-substituted sultines equilibrate with zwitterionic species that react with electron-rich alkenes such as enoxysilanes and allylsilanes, generating beta,gamma-unsaturated silyl sulfinates that can be desilylated and desulfinylated to generate polypropionate fragments containing up to three contiguous stereogenic centers and an (E)-alkene unit. Alternatively, the silyl sulfinates can be reacted with electrophiles to generate polyfunctional sulfones (one-pot, four-component synthesis of sulfones), or oxidized into sulfonyl chlorides and reacted with amines, then realizing a one-pot, four-component synthesis of polyfunctional sulfonamides. Using enantiomerically enriched dienes such as 1-[(R)- or 1-(S)-phenylethyloxyl-2-methyl-(E,E)-penta-1,3-dien-3-yl isobutyrate, derived from inexpensive (R)- or (S)-1-phenylethanol, enantiomerically enriched stereotriads are obtained in one-pot operations. The latter are ready for further chain elongation. This has permitted the development of expeditious total asymmetric syntheses of important natural products of biological interest such as the baconipyrones, rifamycin S, and apoptolidin A.

De Gruyter2008

Total asymmetric synthesis of advanced polyketide fragments of apoptolidinone and rectricticin using new organic chemistry of sulfur dioxide

Cotinica Craita

EPFL2006