Oxacyclic Compounds Research Articles

Various synthetic approaches for [6,7,m]‐tricyclic compounds containing an oxygen‐bridged skeleton

AbstractWe report the synthesis of [6,7,5]‐tricyclic compounds containing an oxabicyclo [3.2.1] octane system from 1,6‐enyne carbonyl. We also synthesized [6,7,6]‐tricyclic compound from 1,7‐enyne carbonyl through Au‐catalyzed cyclization. The synthesis of oxacyclic compounds using iodine or oxygen is environmentally friendly cyclization methods. Oxacyclic compounds are useful for synthesizing various diterpene alkaloids.

Concise synthesis of oxacyclic compounds using highly discriminative two-way transformations of α,β-unsaturated esters in the presence of enones.

Highly discriminative transformation of α,β-unsaturated esters in the presence of enones using two types of phosphonium salts, and their application to the synthesis of oxacyclic compounds in six steps in one pot have been achieved.

Construction of 2,3‐Dihydrofuran Cores through the [3+2] Cycloaddition of Gold α‐Carbonylcarbenoids with Alkenes

Treatment of 2-epoxy-1-alkynylbenzenes with electron-rich alkenes and a [AuCl(PR(3))]/AgX catalyst in CH(2)Cl(2) led to the formation of 2-alkenyl-1-(2,3-dihydrofuran-4-yl)benzenes. This transformation comprises of a gold-catalyzed redox reaction to form a gold alpha-carbonylcarbenoid initially, which then reacts in situ with an alkene in a [3+2] cycloaddition. A range of alkenes are amenable to this tandem reaction, amongst them alpha-substituted styrenes, enol ethers, and 2,3-dimethylbutadienes. Deuterium-labeling experiments suggest a stepwise mechanism for the alpha-carbonylcarbenoid/alkene [3+2] cycloaddition. The resulting 2,3-dihydrofuran products allow access to diverse oxacyclic compounds through a stereoselective ene-oxonium reaction initiated by treatment with HOTf (1 mol %; Tf=trifluoromethanesulfonyl). A stepwise pathway is proposed for this reaction. The feasibility for direct transformation of 2-alkenyl-1-alkynylbenzenes into the desired 2,3-dihydrofuran products through initial m-chloroperbenzoic acid oxidation, followed by the addition of gold catalyst and alkene, has also been demonstrated.

Diversity of Products in the Gold‐Catalyzed Cyclization of 1‐Epoxy‐1‐alkynylcyclopropanes by Using 1‐Oxyallyl Cations

A highly stereoselective AuCl3-catalyzed hydrative cyclization of 1-epoxy-1-alkynylcyclopropanes was observed for cis-epoxides. Since this cyclization produced 1-oxyallyl cations efficiently, we accomplished a two-step [4+2] annulation of epoxyalkynes with dienes and enones, to provide complex oxacyclic compounds with excellent diastereoselectivity (see scheme).

Synthesis of Heterocycle-Annulated Medium-Sized Oxacycles and Lactone Derivative by Intramoleculer Heck Reaction

An efficient and convergent methodology for the highly strained medium-sized oxacyclic compounds and lactone derivatives has been developed via palladium-catalyzed intramoleculer Heck reaction.

ChemInform Abstract: Stereocontrolled Synthesis of Complicated Oxacyclic Compounds via Platinum‐Catalyzed [4 + 2]‐Cycloadditions and Annulations of Enynals with Allylic Alcohols.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Interception of Benzopyrilium Intermediates Yielding Oxacyclic Compounds

Interception of Benzopyrilium Intermediates Yielding Oxacyclic Compounds

Stereocontrolled Synthesis of Complicated Oxacyclic Compounds via Platinum-Catalyzed [4 + 2]-Cycloadditions and Annulations of Enynals with Allylic Alcohols

We report stereoselective synthesis of tricyclic ketals through Pt(II)-catalyzed [4 + 2]-cycloaddition of benzopyrilium/1-en-3-ol functionalities. For nonaromatic enynals, we obtained distinct tricyclic oxacyclic ketones due to occurrence of a new annulation reaction. This work reports the first example that [4 + 2]-cycloadducts are successfully intercepted from such functionalities in diversified approaches. The value of such cycloadditions and annulations are shown by their high diastereoselectivities and chemoselectivities.

Gold-Catalyzed Deoxygenative Nazarov Cyclization of 2,4-Dien-1-als for Stereoselective Synthesis of Highly Substituted Cyclopentenes

Treatment of 2,4-dien-1-als with allylsilanes and PPh(3)AuSbF(6) (3 mol %) led to formation of 1,4-bis(allyl)cyclopentenyl products; this gold catalyst is superior to commonly used Lewis acids according to catalyst screening. Such gold-catalyzed deoxygenative cyclizations are compatible with various oxygen-, amine-, sulfur-, hydrogen-, and carbon-based nucleophiles. The value of this new catalysis is demonstrated by the diverse annulations of 2,4-dien-1-als with electron-rich alkenes and arenes, providing an easy access to complicated cyclopentenyl frameworks. Structural analysis of annulation products reveals evidence for the participation of Nazarov cyclization. This deoxygenative cyclization is extensible to a tandem intramolecular cyclization/nucleophilic addition cascade, giving polycyclic carbo- or oxacyclic compounds with controlled stereochemistry. This new gold catalysis is applied to a short synthesis of natural compounds of the brazilane family, including brazilane, O-trimethyl-, and O-tetramethyl brazilane.

ChemInform Abstract: Reaction of Diols and Triols with Trialkyl Orthoesters: Facile One‐Pot Formation of Oxacyclic Compounds from Triols.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Reaction of Diols and Triols with Trialkyl Orthoesters: Facile One-Pot Formation of Oxacyclic Compounds from Triols

Reaction of diols and triols with trialkyl orthoesters was studied and facile one-pot formation of oxacyclic compound from triols was developed

Dehydroquinate synthase: the use of substrate analogues to probe the early steps of the catalyzed reaction.

The early steps of the proposed mechanistic pathway for dehydroquinate synthase have been probed with a series of substrate analogues. These analogues, 3-9, are structurally prohibited from undergoing the beta-elimination of inorganic phosphate that represents the committed step in the conversion of the substrate 3-deoxy-D-arabino-heptulosonate 7-phosphate (1) to dehydroquinate (2). In agreement with previous observations, the analogues that possess shortened side chains (3,5, and 6) bind more tightly to the enzyme than those (4 and 7-9) that are more nearly isosteric with the substrate. Two hitherto unrecognized factors that influence binding have been identified: (i) carbacylic analogues bind 25-100 times more tightly than the corresponding oxacyclic materials (indeed, the carbacyclic phosphonate 5 has a Ki value of 8 x 10(-10)M) and (ii) the side chain appears to be bound in a gauche conformation similar to the most stable conformation of the cis-vinylhomophosphonate 8. These trends in binding can be rationalized by considering the behavior of the analogues in the first two chemical steps of the mechanism: NAD+-mediated oxidation at C-5 and enolization at C-6 (the first part of the E1cB elimination of inorganic phosphate). Direct spectrophotometric determination of the equilibrium level of enzyme-bound NADH indicates that the carbacyclic analogues are more readily oxidized than the oxacyclic compounds, and this predictable difference in redox behavior is reflected in the observed differences in binding. The gauche conformation of the C-7 side chain appears to be required for proton abstraction from C-6, since only those analogues that can adopt this conformation undergo enzyme-catalyzed exchange of the C-6 proton with the solvent. This conformation positions one of the peripheral oxygens of the phosphate (or phosphonate) group close to the C-6 proton. Taken together with other data, these results suggest that the enzyme exploits this substrate base in the enolization, which occurs through an intramolecular proton transfer. The loss of Pi then completes the beta-elimination.

“The projects that never were”. A lecture given to the polymer discussion group

In reviewing his life's work on the cationic polymerization of alkenes and oxacyclic compounds and the many branch-lines which sprang therefrom, the author emphasizes some of the research projects which did not come to fruition, and speculates on the reasons for the lack of success. A failure in 1946 to initiate a cationic polymerization by high-energy radiation is contrasted with an initially unsuccessful and a subsequent successful attempt in 1955 to use liquid carbon dioxide as a solvent for polymerizing isobutene; it was the much better understanding of the processes involved after the lapse of 9 yr which made the difference. That this, the first-ever use of carbon dioxide as a reaction medium, raised no interest amongst industrialists, despite the cheapness and harmlessness of this solvent, is attributed to the lack of economic incentive.

Chiral Routes to Naturally Occurring Oxacyclic Compounds

Chiral Routes to Naturally Occurring Oxacyclic Compounds

Determination of the basicity of some cyclic ethers and cyclic formals

AbstractThe tendency of some cyclic ethers and cyclic formals (“oxacyclic compounds”) to form protonated complexes was studied by means of UV spectroscopy. The degree of basicity (pKBH+) was evaluated on the basis of the HAMMET indicator functions.The process of complex formation was followed at different values of the HAMMET function in dilute spectroscopically pure sulfuric acid. The pKBH+ values of four of the seven examined compounds correlated very well with the pKBH+ values obtained by a method different in principle. This was taken as an indication of the objectivity of the evaluation of the basicity of the “oxacyclic compounds” by spectral methods regardless of the fact that these compounds are very weak bases and form colourless protonated complexes.

Polymerization of tetrahydrofuran by the AlEt3‐H2O‐promoter system. II. Behavior of promoter in initiation

AbstractThe initiation mechanism of the tetrahydrofuran polymerization catalyzed by the AlEt3–H2O(2:1)‐epichlorohydrin system was studied. The products formed by treatment of the polymerization system at an early stage with sodium methoxide was examined by v.p.c. analysis. It has been shown that the cationic ring‐cleavage of epichlorohydrin i.e., the formation of a cyclic trialkyloxonium ion, constitutes the initiation reaction. This finding is consistent with the assumption of the mechanism for the initiating behavior of reactive oxacyclic compounds according to the proposal “promoter”.