Abstract:In the presence of Me3A1, 1-cyanovinyl acetate added to 2,2'-ethylidenebis[3,5-dimethylfuran] (1) to give a 20:lO: 1 :1 mixture of mono-adducts 4,5,6, and 7 resulting from the same regiocontrol ('para' orienting effect of the 5-methyl substituent in 1). The additions of a second equiv. of dienophile to 4-7 were very slow reactions. The Introduction. -In the preceding report [l], we have disclosed a new synthetic approach to complex and long-chain polypropionates based on the Diels-Alder addition of 2,2'-ethyli… Show more
“…For complex (+)- 22 , two new stereogenic centers are created with the introduction of two hydroxy groups. The two cis hydroxy groups adopt the exo positions on the azanorbornane skeleton, thus supporting the preferential attack of the osmium reagent from the less hindered exo face of the azanorbornyl system 6 Molecular structure of the cationic complex (+)- 22 (thermal ellipsoids at the 50% probability level). 9
“…The absence of coupling between the bridgehead proton H(18) and adjacent endo proton H(19) 13 and the presence of NOE interactions [H(19)−H(18) and H(19)−H(16)] are in agreement with the structure in which the hydroxy group adopts the exo position at C(20). This exo stereochemistry of the hydroxy group is in accord with the preferential attack of the hydroborating agent on the oxanorbornene double bond from the sterically less hindered exo face, followed by stereospecific oxidation with retention of configuration 3 3 Molecular structure of the cationic complex (−)- 9 (thermal ellipsoids at the 50% probability level).
With metal as protection, the introduction of functionalities on coordinated chiral phosphines using
organic transformations was demonstrated. Bis(diphenylphosphino)-substituted oxa- and azanorbornene
metal complexes were subjected to a series of organic transformations including hydrogenation,
hydroboration, electrophilic addition, and dihydroxylation reactions. Hydrogenation of the oxanorbornene
double bond stabilizes the free diphosphino-substituted oxanorbornene ligand, which is otherwise prone
to the retro-cycloaddition reaction. Hydroboration of the oxanorbornenic double bond using borane,
followed by oxidation with alkaline hydrogen peroxide, generated two regioisomeric products with the
introduction of a hydroxy group at the exo position. However, regioselective hydroboration could be
achieved with the use of 9-BBN as the hydroborating agent. Stereoselective electrophilic addition of the
oxanorbornenic double bond with phenylselenenyl chloride resulted in the formation of a sole anti-addition product. Subsequent oxidative syn-elimination of the resultant selenide product was also shown
to proceed regioselectively to give the vinyl chloride complex. Dihydroxylation of the oxa- and
azanorbornenic double bond with osmium tetraoxide proceeded stereoselectively with the introduction
of two hydroxy group at the exo positions. Liberation of the functionalized chiral phosphine ligands
from the metal complexes was also illustrated.
“…For complex (+)- 22 , two new stereogenic centers are created with the introduction of two hydroxy groups. The two cis hydroxy groups adopt the exo positions on the azanorbornane skeleton, thus supporting the preferential attack of the osmium reagent from the less hindered exo face of the azanorbornyl system 6 Molecular structure of the cationic complex (+)- 22 (thermal ellipsoids at the 50% probability level). 9
“…The absence of coupling between the bridgehead proton H(18) and adjacent endo proton H(19) 13 and the presence of NOE interactions [H(19)−H(18) and H(19)−H(16)] are in agreement with the structure in which the hydroxy group adopts the exo position at C(20). This exo stereochemistry of the hydroxy group is in accord with the preferential attack of the hydroborating agent on the oxanorbornene double bond from the sterically less hindered exo face, followed by stereospecific oxidation with retention of configuration 3 3 Molecular structure of the cationic complex (−)- 9 (thermal ellipsoids at the 50% probability level).
With metal as protection, the introduction of functionalities on coordinated chiral phosphines using
organic transformations was demonstrated. Bis(diphenylphosphino)-substituted oxa- and azanorbornene
metal complexes were subjected to a series of organic transformations including hydrogenation,
hydroboration, electrophilic addition, and dihydroxylation reactions. Hydrogenation of the oxanorbornene
double bond stabilizes the free diphosphino-substituted oxanorbornene ligand, which is otherwise prone
to the retro-cycloaddition reaction. Hydroboration of the oxanorbornenic double bond using borane,
followed by oxidation with alkaline hydrogen peroxide, generated two regioisomeric products with the
introduction of a hydroxy group at the exo position. However, regioselective hydroboration could be
achieved with the use of 9-BBN as the hydroborating agent. Stereoselective electrophilic addition of the
oxanorbornenic double bond with phenylselenenyl chloride resulted in the formation of a sole anti-addition product. Subsequent oxidative syn-elimination of the resultant selenide product was also shown
to proceed regioselectively to give the vinyl chloride complex. Dihydroxylation of the oxa- and
azanorbornenic double bond with osmium tetraoxide proceeded stereoselectively with the introduction
of two hydroxy group at the exo positions. Liberation of the functionalized chiral phosphine ligands
from the metal complexes was also illustrated.
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The 1,3-dibromo-5,5-dimethylhydantoin (DBH) was found to efficiently catalyze the one-pot synthesis of highly functionalized tetrasubstituted furan derivatives by the reaction of 1,4-diarylbut-2-ene-1,4-diones and acetoacetates in i-PrOH as the solvent at 80 -908 for 3 -7 h. The products were formed in high yields (82 -95%) under mild and neutral conditions.Introduction. -Substituted furan derivatives are important synthetic intermediates [1] and are found as structural units in many natural products such as in kallolides [2], cembrenolides [3], pheromones [4], and polyether antibiotics [5]. These heterocycles have found applications in many pharmaceuticals, fragrances, and dyes [6]. Furan subunits have also been used as building blocks for a large number of heterocyclic compounds and as synthons in natural-product synthesis [7]. As a consequence, the synthesis [8 -11] and the applications [12 -15] of furan derivatives still attract the attention of organic chemists. The most common strategy involved in the synthesis of furans is the cyclization [16] of 1,4-dicarbonyl compounds. Of the various other methods, syntheses involving transition-metal salts have recently been described for the preparation of substituted furan derivatives [17]. Oh and co-workers [18] have synthesized highly substituted furans via Pt-catalyzed hydroxy-or alkoxy-assisted cyclization of 2-(alk-1-yn-1-yl)alk-2-en-1-ones. More recently, Jaisankar and coworkers reported a novel method for the preparation of highly substituted furans by InCl 3 -catalyzed nucleophilic addition followed by a cyclization reaction, although it was limited to specific substrate classes [19].
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