- Synthesis of the ABC Substructure of Brevenal by Sequential exo-Mode Oxacyclizations of Acyclic Polyene Precursors
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Exploratory studies on the sequential exo-mode oxacyclizations of acyclic polyene precursors have provided a substantial substructure of brevenal, including the fused tricyclic polyether with stereochemical patterns consistent with the AB and BC ring fusions. The synthesis of acyclic substrates featured two variations of Cr(II)/Ni(II) couplings for preparing 1,1-disubstituted allylic alcohols. A sequence of iodine-promoted cycloetherification, base-promoted intramolecular conjugate addition, and mercury-promoted cycloetherification produced the tricyclic substructure.
- Hurtak, Jessica A.,McDonald, Frank E.
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- 8-Endo cyclization of (alkoxycarbonyl)methyl radicals: Radical ways for preparation of eight-membered-ring lactones
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Cyclization of (alkoxycarbonyl)methyl radicals generated from bromoacetates proceeds in the 8-endo made to generate heptanolactones. Three distinct types of 8-endo/5-exo tandem radical cyclizations produce different bicyclic heptanolactones. In certain cases, intramolecular free-radical attack on the heptanolactone carbonyl group initiates further skeletal rearrangement. Ab initio calculations indicate that the preference of the 8-endo cyclization over the 5-exo mode originates from the conformational bias of (alkoxycarbonyl)methyl radicals favoring the Z- over the E-conformation.
- Lee, Eun,Yoon, Cheol Hwan,Lee, Tae Hee,Kim, Sun Young,Ha, Tae Joon,Sung, Yong-Suk,Park, Sang-Hyun,Lee, Sangyoub
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- A Pd-Catalyzed [4 + 2] Annulation Approach to Fluorinated N-Heterocycles
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3-Fluoro- and trifluoromethylthio-piperidines represent important building blocks for discovery chemistry. We report a simple and efficient method to access analogs of these compounds that are armed with rich functionality allowing them to be chemoselectively derivatized with high diastereocontrol.
- García-Vázquez, Víctor,Hoteite, Larry,Lakeland, Christopher P.,Watson, David W.,Harrity, Joseph P. A.
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supporting information
p. 2811 - 2815
(2021/05/05)
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- NOVEL ARGINASE INHIBITORS
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The present invention relates to novel arginase inhibitors of formula (I). These novel compounds are useful in the treatment of diseases that are associated with arginase activity, such as asthma, allergic rhinitis and COPD (chronic obstructive pulmonary disease).
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Page/Page column 15-16
(2020/12/30)
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- POLYMERIZATION OF OLEFINS
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Olefins containing selected functional groups such as silyl, ether and alkenyl, and often containing a blocking group, may be copolymerized with unsubstituted olefins such as ethylene and propylene in the presence of certain coordination compounds of nickel or palladium. The resulting polymers are useful as molding resins, elastomers, in adhesives and for films.
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- Synthesis of L-ascorbic acid derivatives as potential bone remodeling agents taking advantage of the Mitsunobu reaction
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The synthesis of ascorbic acid derivatives 7a-d is described. Starting from alkenylacetates 1a-d subjected to a hydrosilylation reaction, the resulting hydroxy chloro silanes 3a-d were obtained in high yield. The latter compounds were reacted with potassium phthalimide followed with hydrazine hydrate to give the amino silanols 5a-d. Ascorbic acid was then alkylated on its 3-hydroxy position to give 7a-d by means of a Mitsunobu reaction.
- Vila?a, Gil,Rubio, Cyril,Susperregui, Jacques,Latxague, Laurent,Déléris, Gérard
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p. 9249 - 9256
(2007/10/03)
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- Synthesis of 3-sila derivatives of L-ascorbic acid via Mitsunobu reaction
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Various 3-sila derivatives of L-ascorbic acid were synthesized in satisfactory yields. The ether link was formed by an unusual aspect of the Mitsunobu reaction, without the need of protecting the remaining hydroxy groups.
- Rubio, Cyril,Susperregui, Jacques,Latxague, Laurent,Déléris, Gérard
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p. 1910 - 1912
(2007/10/03)
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- Regioselective Synthesis of Hydroxy Sulphides via Trifluoroacetoxysulphenylation of Derivatives of Allylic Alcohols
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Reaction of manganese(III) acetate with diphenyl disulphide in dichloromethane-trifluoroacetic acid in the presence of allylic esters gives trifluoroacetoxy sulphides, which on hydrolysis readily afford vicinal hydroxy sulphides.With acetate esters, neighbouring group participation by the acetate functionality controls the reaction course.Thus regiospecific addition to allyl acetate affords after hydrolysis only 3-phenylthiopropane-1,2-diol.In contrast, with trifluoroacetate esters the inductive effects of the trifluoroacetate functionality lead to a different regiocontrol.Thus addition of diphenyl disulphide to allyl trifluoroacetate gives after hydrolysis only 2-phenylthiopropane-1,3-diol.The regio- and stereochemistry of addition to a variety of other allylic (and homoallylic) esters is described and the extension of this type of regiocontrol is discussed.
- Samii, Zakaria K. M. Abd El,Ashmawy, Mohamed I. Al,Mellor, John M.
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p. 2509 - 2516
(2007/10/02)
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- Transformation of Carbon-Oxygen into Carbon-Carbon Bonds Mediated by Low-Valent Nickel Species
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The substitution of alkoxy groups of enol ethers (1-methoxycyclohexenes, 1-methoxy-1-alkenes, and benzofuran) and aryl ethers (methoxynaphthalenes, cresyl methyl ethers, and dimethoxybenzenes) by hydrogen, alkyl groups, and aryl units, through Grignard reactions catalyzed by bis(triphenylphosphine)nickel dichloride or nickel dichloride, is described.The stereochemistry of the new reaction is portrayed, especially in connection with processes involving ring opening of dihydropyrans and dihydrofurans.The reaction has been applied to the synthesis of a termite trail pheromone and the acetate of the Douglas fir beetle aggregation pheromone.
- Wenkert, Ernest,Michelotti, Enrique L.,Swindell, Charles S.,Tingoli, Marco
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p. 4894 - 4899
(2007/10/02)
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- Convenient Synthetic Route tp 6,8-Dioxabicyclooctanes, the Aggregation Pheromone Components of Bark Beetles
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Convenient syntheses of (+/-)-frontalin (I) and (+/-)-brevicomins (IIa) and (IIb) were achieved from pent-4-en-1-ol (2) and pent-4-yn-1-ol (3).In a few simple and unambiguous steps, the alkenol (2) and the alkynol (3) were transformed into the acetal bromide (7) and the alkenyl bromides (14) and (17), respectively.Acylation of Grignard reagents of these bromides provided the corresponding methyl ketones (8), (15), and (18), the key intermediates for the synthesis of the title bicyclic acetals.The ketone (8) was converted into the olefin (9) which, on epoxidation followed by acid hydrolysis, yielded (+/-)-frontalin, whereas epoxidation of the alkenones (15) and (18) and subsequent cyclization afforded exo- and endo-brevicomin, stereoselectively.
- Joshi, Navalkishore N.,Mamdapur, Vasant R.,Chadha, Mohindra S.
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p. 2963 - 2966
(2007/10/02)
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- Solvomercuration-Demercuration. 8. Oxymercuration-Demercuration of Methoxy-, Hydroxy-, and Acetoxy-Substituted Alkenes
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The oxymercuration-demercuration (OM-DM) of a series of methoxy-, hydroxy-, and acetoxy-substituted alkenes was examined.The systems examined were the allyl, crotyl, 3-buten-1-yl, 4-penten-1-yl, and 5-hexen-1-yl.The methoxyalkenes undergo hydration with very high regioselectivity and almost quantitative yield in all cases.However, a small -I effect is observed in the case of the allylalkene (97.1percent Markovnikov vs. 99.5percent in 1-hexene).Moreover, in the crotyl case, a major directing effect is observed: 97.7percent 3-ol, 2.3percent 2-ol.The other three alkenes undergo the OM reaction with no effect from the methoxy group (99.5percent Markovnikov isomer).In contrast, only allyl-, crotyl-, and 3-buten-1-yl alcohols produce major amounts of hydrated products, the diols.While no hydroxyl group directing effect is observed in the allyl system, a major one is again seen in the case of the crotyl: 93.5percent l,3-diol and 6.5percent l,2-diol.The major products from the 4-penten-1-yl and 5-hexen-1-yl and alcohols are 2-methyltetrahydrofuran and 2-methyltetrahydropyran, respectively, resulting from OH-5 and OH-6 neighboring group participation in the OM stage.The acetoxy alkenes undergo hydration to give diols in ca. 80percent yield with ca. 20percent unreacted starting material.This is the result of a competitive deoxymercuration reaction which is occurring in the DM stage.However, the yield of hydrated products can be increased by varying the amount of base used in the DM.Neighboring-group participation, AcO-5, is observed in the allyl system only, resulting in a 65percent yield of the Markovnikov oxymercurial, by 1H NMR analysis, and a 35percent yield of the acetoxy-exchanged mercurial.Again, a major -I-directing effect of the acetoxy group was observed in the crotyl system but not in the others.In addition to the expected l,2- and l,3-diols, the OM-DM of crotyl acetate also resulted in small amounts of the unexpected 2,3-diol under kinetic conditions.Finally, a modified DM procedure has been developed which is compatible with the acetoxy group.
- Brown, Herbert C.,Lynch, Gary J.
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p. 531 - 538
(2007/10/02)
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- METATHESE D'ACETATES D'ALCOOLS ω-INSATURES. SYNTHESE DE PHEROMONES D'INSECTES
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Esters of alkenoic acids, including insect pheromones as examples, have been synthesized using alkene metathesis reactions.
- Levisalles, Jaques,Villemin, Didier
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p. 3181 - 3186
(2007/10/02)
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