Lewis Acid-catalyzed Rearrangement Research Articles

Proposed mechanism for the reaction catalyzed by a diterpene cyclase, aphidicolan-16beta-ol synthase: experimental results on biomimetic cyclization and examination of the cyclization pathway by ab initio calculations.

To examine the mechanism of the cyclization reaction catalyzed by aphidicolan-16beta-ol synthase (ACS), which is a key enzyme in the biosynthesis of diterpene aphidicolin, a specific inhibitor of DNA polymerase alpha, skeletal rearrangement of 2a and biomimetic cyclization of 4b were employed. The structures of the reaction products, which reflect penultimate cation intermediates, allowed us to propose a detailed reaction pathway for the Lewis acid-catalyzed cyclizations and rearrangements. Isolation of these products in an aphidicolin-producing fungus led us to speculate that the mechanism of the ACS-catalyzed cyclization reaction is the same as that of a nonenzymatic reaction. Ab initio calculations of the acid-catalyzed reaction intermediates and the transition states indicate that the overall reaction catalyzed by ACS is an exothermic process though the reaction proceeds via an energetically disfavored secondary cation-like transition state. In conjunction with the solvent effect in the acid-catalyzed reactions, this indicates that the actual role of ACS is to provide a template which enforces conformations of the intermediate cations leading to the productive cyclization although it has been believed that the cation-pi interaction between cation intermediates and aromatic amino acid residues in the active site is important for the enzymatic catalysis. This study provided important information on the role of various cationic species, especially secondary cation-like structures, in both nonenzymatic and enzymatic reactions.

The Si−Ge Bond: Rearrangements, Migrations, and Cleavages

1-Chloropentamethyl-1-silylgermane, ClSiMe2GeMe3 (1), and 1-chloromethylpentamethyl-1-silylgermane, ClCH2SiMe2GeMe3 (2), undergo Lewis acid-catalyzed rearrangements to ClGeMe2SiMe3 (3) and ClSiMe2CH2GeMe3 (4), respectively. Under similar conditions the isomeric ClGeMe2SiMe3 (3) undergoes a fragmentation reaction involving the formation of Me3SiCl and Me2GeCl2, and ClCH2GeMe2SiMe3 (5) rearranges to ClMe2GeCH2SiMe3 (6). Methyllithium treatment of Ph3SiGeMe3 and Me3SiGePh3 and [1,1‘]-tetramethylsilylgermylferrocenophane [(1,1‘-Me2SiMe2Ge((η5-C5H4)2Fe] results in methylation of the silicon atom and formation of the corresponding germyl anion. When the silicon−germanium-bonded fragment is incorporated into a bimetallic transition metal complex, i.e., (η5-C5H5)Fe(CO)2SiMe2GeMe2Fe(η5-C5H5)(CO)2 (7), base treatment with 1 equiv of lithium diisopropylamide (LDA) leads to predominance of silyl group migration to the cyclopentadienyl ring over germyl migration (9:1). Treatment of 7 with a 2.5 molar excess of LDA, fo...

Regio- and Stereoselective Synthesis of beta-D-Gluco-, alpha-L-Ido-, and alpha-L-Altropyranosiduronic Acids from Delta(4)-Uronates.

The stereoselective synthesis of beta-D-glucopyranosiduronic, alpha-L-idopyranosiduronic, and alpha-L-altropyranosiduronic acids has been performed from different Delta(4)-uronate monosaccharides. Bromination of the C-4,5 double bond provided the trans-diaxial bromohydrin derivatives, which were converted to the corresponding epoxides in high yields. Direct reduction of the epoxides using borane-tetrahydrofuran complex led to the corresponding glucuronic acids in low to good yields. Glucuronic acids were also obtained in satisfactory yields through a two-steps procedure involving bromination of the epoxide with titanium(IV) bromide followed by reduction using tributyltin hydride. Lewis acid-catalyzed rearrangement of these epoxides led to the corresponding alpha-L C-4 ketopyranosides adopting the (1)C(4) chair conformation. Hydride reduction afforded the alpha-L-idopyranosiduronic or the alpha-L-altropyranosiduronic acids, the stereoselectivity of the reduction being controlled by the appropriate substitution pattern.

Novel Lewis Acid-Catalyzed Rearrangement of a Sugar-Base Hybrid to Afford an Anhydronucleoside

Treatment of the sugar-base hybrid 9 with boron trichloride at low temperature for 40 h affords the 6,3′-anhydro-2′-deoxyuridine 10 in 40% yield (80% based on recovered 9) via a novel structural rearrangement.

Synthesis of Glycoside Derivatives Employing the Ferrier Rearrangement1

Various glycals underwent smooth Lewis acid-catalysed allylic rearrangement reactions with O-nucleophiles to yield 2,3-unsaturated glycoside derivatives. In the hexose series predominantly α-D-, and in the pentose series β-D-anomers resulted. Among others Ω-cyano- as well as Ω-benzyloxycarbonylamino functionalised alcohols could be used successfully. With diols the corresponding 1,1′-bridged disaccharides could be obtained. 1. Dedicated to the memory of Prof. Akira Hasegawa.

A novel synthesis of chain-extended amino sugar derivatives through aza-Cope rearrangement of N-galactosyl- N-homoallylamines

Abstract Chain-extended amino sugars are synthesized via stereocontrolled Lewis acid-catalyzed aza-Cope rearrangement of N-glycosyl homoallylamines in high yield and stereoselectivity.

Conversion of a gibberellin aldehyde into a 20-norkaurenoid lactone

The Lewis acid-catalysed rearrangement of a 6β-hydroxy-gibberellin-7α-carboxaldehyde results in ring-expansion of the 5-membered B-ring of the gibberellin molecule to afford access to highly functionalised 20-norkaurenoids.

Cycloaddition of Cyclopentadiene to 3-Deoxy-1,2:5,6-di-O-isopropylidene-alpha-D-erythro-hex-3-enofuranose. Synthesis and Representative Chemistry of 1,6-Anhydro-2,3-dideoxy-beta-D-glycero-hex-2-enopyran-4-ulose ("Isolevoglucosenone").

Treatment of D-glucose-derived alkene 4 with cyclopentadiene in the presence of a Lewis acid results in the formation of cycloaddition products 8-11. Evidence is presented to show that these 1,6-anhydro sugar-cyclopentadiene adducts do not arise from rearrangement of 4 to isolevoglucosenone (5) followed by cycloaddition but are the result of Lewis acid-catalyzed rearrangement of alkene 4 to acyclic dienophile 12 followed by addition of cyclopentadiene. Major cycloadduct 8 has been utilized as a source of the enantiomerically pure carbocycles 14-25 by manipulation of the alkene and ketone functions and cleavage of the 1,6-anhydro bridge. In the absence of diene, alkene 4 undergoes rearrangement to enone 5 in 32% yield. Reaction of 5 with several dienes results only in the formation of "bottom-face" adducts 10,11, 28, and 29, and conjugate addition of either HN(3) or Me(3)COOH is found to be completely stereoselective to afford 30 and 31, respectively. Subsequent manipulation of azide 30 leads to precursors of several naturally occurring 2-amino-2,3-dideoxy sugars.

Thermal electrocyclic spirocyclization of p-benzoquinone imines: A novel synthetic route to trifluoromethylated spirodiazacarbocycles

Electrochemically prepared N-(4-oxo-2,5-cyclohexadiene-1-ylidene)-2,2,2-trifluoroethanimidamides (p-benzoquinone derivatives) (2) cyclized on heating in DMSO at 120 °C to 2′-trifluoromethyl-spiro[2,5-cyclohexadiene-1,4′-1H(or 3H)-quinazolin]-4-ones (spirodienone derivatives) (3) and (4), which were transformed to 1,3-diazepine derivative (7) by Lewis acid-catalyzed dienone-phenol rearrangement.

Aminium salts catalyzed rearrangement of α-pinene and β-ionone oxides

β-ionone and α-pinene oxides 1, 3 isomerize rapidly and selectively to 1-(1,2,2-trimethylcyclopent-1-yl)-pent-2-en-1,4-dione 2 and the industrialy important 2,2,3-trimethyl-3-cyclopentene acetaldehyde 4. under the influence of catalytic amounts of aminium salts A,B. In order to find insights into the mechanism of our procedure, protic and Lewis acid-catalyzed rearrangements have also been reconsidered.

An Unusual Acid-catalyzed Rearrangement of 1,2,4-Trioxanes

A new Lewis acid-catalyzed rearrangement of the peroxide group in two 1,2,4-trioxanes, deoxoartemisinin and 12β-allyldeoxoartemisinin, yielding ring enlarged oxide, is described

The synthesis of an asparenomycin analog

The synthesis of an analog of the carbapenem antibiotics, the asparenomycins, is described. This analog lacks the methyl group in the 6-alkylidene side chain while a methyl group has been placed at the 1β-position. The key step involved the Lewis acid-catalyzed rearrangement of an epoxide to an allylic alcohol.

Isomer selectivity in stereocontrolled Payne rearrangement–epoxide cleavage of 2,3-epoxy alcohols in aprotic solvents: application to an enantioselective total synthesis of (+)-exo-brevicomin

Organo-copper and -cuprate reagents may be used to trap the more reactive epoxy alkoxide isomer in a Lewis acid-catalysed Payne rearrangement process. This methodology has been used as the key step in a five-step enantioselective total synthesis of (+)-exo-brevicomin, an aggregation pheromone of the Western Pine beetle Dendroctonius brevicomis.

A novel method for the synthesis of anomerically allylated C-glycofuranosides. An unusual Lewis acid-catalysed rearrangement of an oxetanosyl-N-glycoside to furanosyl-C-glycosides

An oxetanosyl-N-glycoside is converted into furanosyl-C-allylglycosides with allyltrimethylsilane in the presence of Lewis acid.

New approach to C-aryl glycosides starting from phenol and glycosyl fluoride. Lewis acid-catalyzed rearrangement of O-glycoside to C-glycoside

C-Glycosidation of phenols is achieved by treatment of glycosyl fluoride with phenolic compound under Lewis acidic conditions, which leads to initial O-glycoside formation followed by rearrangement to C-congener. Cp 2HfCl 2-AgClO 4 is particularly effective for this conversion.

Application of the Lewis acid-catalysed Claisen rearrangement of 4′-(1,1-dimethylallyloxy) coumarates to the synthesis of demethylsuberosin

The synthesis of the linear coumarin demethylsuberosin (1) is described via regioselective boron trifluoride–diethyl ether-catalysed Claisen rearrangement of methyl 2′-benzyloxy-4′-(1,1-dimethylallyloxy)cinnamate (4c).

Preparation and cleavage reactions of some steroidal epoxides

The steroidal epoxides (12), (13), (28), and (34) have been prepared and their reactions investigated. Attempts to prepare the epoxides (12) and (13) by the action of dimethylsulphonium methylide or dimethylsulphoxonium methylide on the ketone (1) gave instead the rearranged product (2) and its methyl ether (3). Compound (2) has also been obtained by base-catalysed isomerisation of the spiro-epoxide (13). Lewis acid-catalysed rearrangement of the epoxides (12), (28), and (34) into the A-homo-B-norsteroids (16), (29), and (43) respectively is described.

Threefold transannular epoxide cyclization. Synthesis of a heterocyclic [formula omitted]17-hexaquinane

The Lewis acid-catalyzed rearrangement of two [3.3.3]propellane triepoxides to a heterocyclic C 17-hexaquinane derivative is described.

ChemInform Abstract: LEWIS ACID‐CATALYZED REARRANGEMENT OF GLUT‐5‐EN‐3β‐YL ACETATE AND GLUT‐5(10)‐EN‐3β‐YL ACETATE

Chemischer InformationsdienstVolume 10, Issue 26 Natural Products ChemInform Abstract: LEWIS ACID-CATALYZED REARRANGEMENT OF GLUT-5-EN-3β-YL ACETATE AND GLUT-5(10)-EN-3β-YL ACETATE A. CHATTERJEE, A. CHATTERJEESearch for more papers by this authorS. K. SAHA, S. K. SAHASearch for more papers by this authorS. MUKHOPADHYAY, S. MUKHOPADHYAYSearch for more papers by this author A. CHATTERJEE, A. CHATTERJEESearch for more papers by this authorS. K. SAHA, S. K. SAHASearch for more papers by this authorS. MUKHOPADHYAY, S. MUKHOPADHYAYSearch for more papers by this author First published: June 26, 1979 https://doi.org/10.1002/chin.197926349Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume10, Issue26June 26, 1979 RelatedInformation

Photocycloadditions of p-quinones to ketenimines

Photo-induced cycloadditions of p-benzoquinone derivatives and 1,4-naphthoquinone to several ketenimines afforded 1 : 1 adducts. Two consecutive adducts, 2-imino-1-oxaspiro [3.5] nona-5,8-dien-7-ones and 1-aza spiro[3.5]nona-5,8-diene-2,7-diones, were obtained from these photolyses in moderate yields. Their structures, which had been postulated as intermediates in a similar reaction, were determined by physical and chemical methods. These two types of spiro-cyclohexa-2,5-dienone gave the rearranged products, 2,3-dihydro-5-hydroxy benzofuran-2-imines and 5-hydroxyindolin-2-ones, respectively, by Lewis-acid catalysed rearrangement.