1,721,009 research outputs found
A Bicyclo[3.2.0]hept-3-en-6-one Approach to Prostaglandin Intermediates
No full text[GRAPHICS]The substituted cyclopentanic structures, 6-benzyloxymethyl-7-hydroxy-2-oxabicyclo (1), a Corey lactone derivative, and 6-exo-benzyloxymethyl-2-oxabicyclo[3.3.0]oct-7-en-3-one (2), have been obtained stereoselectively through the bicyclo[3.2.0]hept-3-en-6-one approach via 5-benzyloxymethyl-3-hydroxy-6-heptenoic acid, easily accessible from the inexpensive monoprotected cis-2-butene-1,4-diol
The Bicyclo[3.2.0]heptan-endo-2-ol and Bicyclo[3.2.0]hept-3-en-6-one Approaches in the Synthesis of Grandisol: The Evolution of an Idea and Efforts to Improve Versatility and Practicality
No full textIn this paper we will disclose a chemistry story that started with a single molecule, the monoterpene grandisol, used in protecting cotton crops from an important pest, Anthonomus grandis Boheman, Initially, efforts were aimed at giving ever more practicality, versatility, and efficiency to a synthetic scheme that was centered on the key role of the 2,5- dimethylbicyclo[3.2.0]heptan-endo-2-ol, available from intermolecular photocyclization and methylation or, better and more conveniently, by an intramolecular copper(I) catalyzed photo-bicyclization of the 3,6-dimethylhepta-1,6-dien-3-ol. We have developed an enantiospecific synthesis of both enantiomers of grandisol although some drawbacks would preclude scale up and commercialisation, The major Limits of this original single-target synthetic scheme are pointed out along with the changed landscape resulting from recent developments in the fields of bioorganic chemistry and entomology, These changes prompted the elaboration of a new strategy focused on the conception and the development of a practical and efficient preparation bicyclo[3.2.0]hept-2-en-6-ones. The "bicyclo[3.2.0]hept-2-en-6-one approach" stems from a very convenient and general preparation, without photochemical steps, of bicyclo[3.2.0]hept-2-en-6-ones. These compounds proved to be amenable to selective manipulations to prepare not only grandisol but also other important molecules such as lineatin, filifolone, and raikovenal in multitarget and versatile synthetic schemes. Moreover, through resolution of the bicyclo[3.2.0]hept-2-en-6-ones, the procedures can be used to produce enantiomerically pure products. The bismethylation of the carbon atom adiacent to the carbonyl group as well as the conversion into the corresponding unsaturated bicyclic lactones are two important reactions that amplify the potential utility of bicyclo[3.2.0]hept-2-en-6-ones. Their peculiar reactivity, ascribed to the fact that the carbonyl group and the carbon-carbon double bond are attached to the same bridge-head carbon atom, has been demonstrated by the high chemio-, regio-, and stereoselectivity of the NBS-induced lactonization
Synthesis of 5-Acyl-3-(ethoxycarbonyl)-2-isoxazolines 2-Oxides by a Tandem Conjugate Addition-Ring Closure of Ethyl Nitroacetate with .alpha.-Bromo Enones
No full textSynthesis of 5-Acyl-3-(ethoxycarbonyl)-2-isoxazolines 2-Oxides by a Tandem Conjugate Addition-Ring Closure of Ethyl Nitroacetate with α-Bromo Enone
Silicon-Tethered 1,3-Dipolar Cycloaddition of 4-Hydroxy-2-isoxazoline 2-Oxides
No full textSilicon-tethered 1,3-dipolar cycloaddition of 4-hydroxy-2-isoxazoline 2-oxide
Stereoselective synthesis of 3-(ethoxycarbonyl)-4-hydroxy-5-(1-hydroxyalkyl)-2-isoxazoline 2-oxides by reaction of 2,3-epoxy aldehydes and ethyl nitroacetate on alumina surface
No full textTreatment of racemic 2,3-epoxy aldehydes and ethyl nitroacetate with alumina affords title compounds through a nitroaldol reaction—cyclization process. While in the case of 3-trans-monosubstituted substrates, C4,C5-trans and cis isomers (dr = 1.5) with C5,C6-anti configuration are obtained, 3-cis-monosubstituted 2,3-epoxy aldehydes give C4,C5-trans and cis derivatives with a much higher diastereoselectivity (dr > 20) and C5,C6-syn configuration. 5-Exo cyclization occurs also when 2,3-epoxy aldehydes are 2-substituted
d-Mannitol as the Chiral Source for the EPC Synthesis of Both Enantiomers of 3-Ethoxycarbonyl-4-hydroxy-2-isoxazolines and Highly Functionalized Tricyclic Systems
No full textThe EPC preparation of both enantiomers of cis- and trans 5-substituted 4-hydroxy-2-isoxazoline 2-oxides has been achieved in an enantiodivergent fashion starting from D-mannitol through the application of the tandem nitroaldol-cyclization reaction to enantiomerically pure alpha-mesyloxyaldehydes. These stereochemically labile aldehydes have been generated in situ and reacted under very mild domino conditions. Enantiomeric purity of the products has been assessed by H-1 NMR and HPLC analyses of the corresponding Mosher's esters. The enantiomerically pure 4-hydroxy-2-isoxazoline a-oxides have been employed as pivotal intermediates for the EPC preparation of the corresponding deoxygenated derivatives and highly functionalized tricyclic systems (HFTS) 1, useful for the preparation of 2-aminopolyols and alpha,alpha-disubstituted polyhydroxy amino acids
Resolution and EPC synthesis of both enantiomers of 2,5-Dimethylbicyclo[3.2.0]heptan-endo-2-ol, Key Intermediate in the Synthesis of Grandisol
No full textThe pure enantiomers of 2,5-dimethylbicyclo[3.2.0]heptan-endo-2-ol, key intermediate in the synthesis of grandisol, have been conveniently prepared by optical resolution with (2S)-(-)-and (2R)-(+)-1-(4-toluenesulphonyl)pyrrolidine-2carboxylic acid chloride (NTP-Cl) as resolving agents, and by an EPC synthesis employing commercially available (3R)-(-)-and (3S)-(+)-linalool as chiral sources
Stereocontrolled synthesis of 3-(ethoxycarbonyl)-4-hydroxy-2-isoxazoline-2-oxides. A new approach to the synthesis of 4-hydroxylated 2-isoxazolines
No full textTreatment of 2-bromo aldehydes and ethyl nitroacetate with alumina without solvent, or in solution with a tertiary base, at room temperature gives the diastereoisomeric title compounds in fair yields by a tandem nitroaldol reaction-cyclization sequence opening a new route for the preparation of trans and cis 4-hydroxylated 2-isoxazolines in a predictable way
Consecutive and domino processes for the synthesis of a heavily functionalised tricyclic system
No full textOne pot multi-bond forming reactions are one of the ways to address the ever growing demand for efficiency in organic synthesis that concern the chemical community. This paper presents a new three-component domino process that efficiently combines four bond-forming reaction steps into a single synthetic operation. From easily available linear starting materials and under very mild conditions, this process builds five new bonds and four new chiral centers, giving rise to the selective formation of a new class of fused heteroatomic tricyclic system, which may be exploited for the synthesis of biologically interesting aminopolyhydroxylared compounds. (C) 1998 Elsevier Science Ltd. All rights reserved
A new, effective route to methyl substituted 3,3a,4,6a-tetrahydro-2H-cyclopenta[b]furan-2-ones
No full text3,3a,4,6a-Tetrahydro-2H-cyclopenta[b]furan-2-ones 1, important starting materials in the synthesis of linear condensed triquinane sesquiterpenes, have been prepared in an efficient manner by an effective bicyclization of 3-hydroxy-6-heptenoic acids, followed by a Baeyer-Villiger oxidation of the bicyclo[3.2.0]hept-3-en-6-one intermediates
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