- The First Examples of Nonenzymic, Biomimetic Polyene Pentacyclizations. Total Synthesis of the Pentacyclic Triterpenoid Sophoradiol
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The first examples of nonenzymic, biomimetic, polyene pentacyclizations are reported.A series of closely related (E,E,Z,Z)-polyenes 10-13 with the same tetraene carbon backbone but with differing initiator groups were synthesized and cyclized.The polyenes
- Fish, Paul V.,Johnson, William S.
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- Enantioselective synthesis of 1(R)-trans-Chrysanthemic acid
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1(R)-trans-Chrysanthemic acid has been prepared in four steps from methyl 5-methyl-2,4-hexadienoate and isopropylidene diphenylsulfurane.
- Krief, Alain,Provins, Laurent,Froidbise, Alexandre
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- Optically active nitroalkenes - Synthesis, addition reactions and transformation into amino acids
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Optically active nitroalkenes 4 were synthesized via Henry reaction. Conjugate addition of vinylmagnesium bromide to 4 gave nitroalkane syn-5 while cyclopropanation with sulfur ylides or dibromocarbene afforded nitrocyclopropanes 8, 10 and 11 in a diaster
- Hübner, Jan,Liebscher, Jürgen,P?tzel, Michael
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p. 10485 - 10500
(2007/10/03)
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- Regioselectivity of Rhodococcus NCIMB 11216 epoxide hydrolase: Applicability of E-values for description of enantioselectivity depends on substrate structure
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The regioselectivity of purified epoxide hydrolase from Rhodococcus NCIMB 11216 was investigated by hydrolyzing a series of structurally different epoxides 1a-5a in 18O-labelled water followed by GC/MS analysis of the 1,2-diols formed 1b-5b. Th
- Mischitz,Mirtl,Saf,Faber
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p. 2041 - 2046
(2007/10/03)
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- Diastereoselective cyclopropanations of chiral bicyclic lactams leading to enantiomerically pure cyclopropanes. Application to the total synthesis of CIS-(1S, 3R)-deltamethrinic acid and R-(-)- dictyopterene C
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A novel diastereoselective cyclopropanation based on readily available chiral bicylic lactams (1b-c, 6a-b) has provided a number of enantiomerically pure cyclopropanes. Cyclopropanations of unsaturated lactams (10a-h, 12-14) were performed using sulfur ylides as well as a 3+2 cycloaddition-photolysis sequence and furnished the desired cyclopropane adducts (16, 17, 19, 22) in fair to excellent yields. In all cases involving sulfur ylides, cyclopropanations proceeded with a high degree of exo/endo diastereoselectivity (>;90%). However, the mode of addition, exo vs endo, was found to be highly dependent on the angular substituent of the unsaturated lactam. In the case of diazoalkane cycloadditions, high regioselectivity was observed in all cases although exo/endo selectivity was governed by the diazoalkane employed. Diazoisopropane, being more reactive than diazomethane, normally led to lower diastereomeric ratios. Minor diastereomers could be readily removed by chromatography or in most cases by a single recrystallization to provide diastereomerically pure cyclopropyl bicyclic lactams (16, 17, 19, 22). Applications of this methodology to compounds of biological significance was exemplified by an asymmetric, total synthesis of cis-(1S, 3R)-deltamethrinic acid (34) and R-(-)- dictyopterene C′ (42) in high enantiomeric purity.
- Romo, Daniel,Romine, Jeffrey L.,Midura, Wanda,Meyers
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p. 4951 - 4994
(2007/10/02)
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- STEREOSELECTIVE SYNTHESIS OF METHYL (1R) TRANS- AND (1R) CIS-HEMICARONALDEHYDES FROM NATURAL TARTARIC ACID: APPLICATION TO THE SYNTHESIS OF S-BIOALLETHRIN AND DELTAMETHRIN INSECTICIDES.
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Very efficient enantioselective syntheses of (1R)-trans-and cis-hemicaronaldehydes precursors of (1R)-trans chrysanthemic acid and its (1R)-cis dibromovinyl analogue starting from natural tartaric acid or D-mannitol are described.They are based on the rea
- Krief, A.,Dumont, W.,Pasau, P.,Lecomte, Ph.
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p. 3039 - 3052
(2007/10/02)
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- The Bicycle Rearrangement. Relationship to the Di-?-methane Rearrangement and Control by Bifunnel Distortion. Mechanistic and Exploratory Organic Photochemistry
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The generality of the bicycle rearrangement was extended and the mechanism was further investigated by study of the photochemistry of 3,4-benzo-2-methylene-6,6-dimethylbicyclohex-3-ene, 2,2-dimethyl-1-methylene-1,2-dihydronaphthalene, 4,4-dimethyl-1-methylene-1,4-dihydronaphthalene, 2,2-dimethylspiro, and 1,1-dimethyl-2-methylene-1,2-dihydronaphthalene.Direct irradiation of the benzobicyclohexene led to the spiroindene as the major product with a quantum yield of 0.040.The minor photoproduct was the 2,2-dimethyldihydronaphthalene, formed with a quantum yield of 0.0033.Both products arise from a mechanism in which the isopropylidene moiety bicycles along the 1-methylenindene ? system.The 2,2-dimethyldihydronaphthalene derives from an intermediate cyclopropyldicarbinyl diradical, arising in the bicycling process, opening its three ring.Irradiation of the 2,2-dimethyldihydronaphthalene led exclusively to the benzobicyclohexene without formation of the spiroindene isomer; the efficiency here was 0.086.This reaction is only formally the reverse of the benzobicyclohexene photolysis and utilizes a different state of the cyclopropyldicarbinyl diradical as an intermediate.The lack of formation of spiroindene product from the 2,2-dimethyldihydronaphthalene is discussed in terms of a distorted bifunnel effect.The photolysis of the 4,4-dimethyldihydronaphthalene led to the benzobicyclohexene with an efficiency of 0.22; here, again, a bicycle mechanism is used.The spiroindene isomer and the 1,1-dimethyldihydronaphthalene were unreactive.Also, the triplets throughout were unreactive.Singlet excited state rate constants were derived for each of the reactions.Correlation diagrams, consisting of a triptych with benzobicyclohexene, dihydronaphthalene, and spiro compound at the three branches, reveal a HOMO-LUMO crossing on the benzobicyclohexene branch.The positioning of the crossing, again, accounts for the unidirectionality of the reactions.At the SCF-CI level a distorted bifunnel was encountered and the hypersurfaces concur in predicting the photochemistry.The distorted funnel concept was developed along with other related photochemical theory.
- Zimmerman, Howard E.,Factor, Ronda E.
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p. 3538 - 3548
(2007/10/02)
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