Bicyclic Ketals Research Articles

Introduction of Bicyclic Ketal Chemistry: Synthesis and Transformation Reaction of 6,8‐Dioxabicyclo[3.2.1]octane Skeletal System

AbstractFor Abstract see ChemInform Abstract in Full Text.

Enantioselective total synthesis of (+)-leucascandrolide A macrolactone.

[reaction: see text] The enantioselective synthesis of the (+)-leucascandrolide A macrolactone has been achieved in 20 linear steps from 1,3-propanediol. The key steps in the synthesis are a reductive cleavage of bicyclic ketal 5 to establish the C15 stereogenic center and a diastereoselective aldol of the boron enolate of methyl ketone 3 to aldehyde 4 in preparation for a heteroconjugate addition for the introduction of the C3 stereocenter.

Frontalin: a chemical message of musth in Asian elephants (Elephas maximus).

Musth is an important male phenomenon affecting many aspects of elephant society including reproduction. During musth, the temporal gland secretions (as well as the urine and breath) of adult male Asian elephants (Elephas maximus) discharge a variety of malodorous compounds together with the bicyclic ketal, frontalin. In contrast, teenage male elephants in musth release a sweet-smelling exudate from their facial temporal gland. We recently demonstrated that the concentration of frontalin becomes increasingly evident as male elephants mature. In the present study, we demonstrate that behaviors exhibited towards frontalin are consistent and dependent on the sex, developmental stage and physiological status of the responding conspecific individual. To examine whether frontalin functions as a chemical signal, perhaps even a pheromone, we bioassayed older and younger adult males, and luteal- and follicular-phase and pregnant females for their chemosensory and behavioral responses to frontalin. Adult males were mostly indifferent to frontalin, whereas subadult males were highly reactive, often exhibiting repulsion or avoidance. Female chemosensory responses to frontalin varied with hormonal state. Females in the luteal phase demonstrated low frequencies of responses, whereas pregnant females responded significantly more frequently, with varied types of responses including those to the palatal pits. Females in the follicular phase were the most responsive and often demonstrated mating-related behaviors subsequent to high chemosensory responses to frontalin. Our evidence strongly suggests that frontalin, a well-studied pheromone in insects, also functions as a pheromone in the Asian elephant: it exhibits all of the determinants that define a pheromone and evidently conveys some of the messages underlying the phenomenon of musth.

Introduction of Bicyclic Ketal Chemistry: Synthesis and Transformation Reaction of 6,8-Dioxabicyclo[3.2.1]octane Skeletal System

A stereo- and regioselective bicyclic ketal synthesis and several facile one-pot transformations of bicyclic ketals are described with plausible mechanisms. Products have included 6,£-unsaturated ketones, mono- and diacetoxy ketones, transketalized ketones, cis- and trans-cyclic ethers, 1,5-diketones, cis-1,2-cyclopentanediols, 2,6-disubstituted pyridines, 2,3,6-trisubstituted pyridines, and conjugated and nonconjugated cyclohexenones.

Synthesis of the C1-side chain of zaragozic acid D and progress towards a total synthesis

A synthesis of a 1,3-dithiane corresponding to the C1-side chain of zaragozic acid D is described. An aldol reaction using an Evans oxazolidinone is the key step in controlling stereochemistry. Metallation of the derived dithiane monosulfoxide and coupling to an aldehyde effected construction of the C1–C7 bond. Subsequent steps are also reported, including acid-mediated ketalization resulting in formation of an advanced synthetic intermediate containing the bicyclic ketal core of the natural product.

ChemInform Abstract: Synthesis of a 2,9‐Dioxabicyclo[3.3.1]nonane via Double Intramolecular Hetero‐Michael Addition: Entry to the F—G Ring System of the Azaspiracids.

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.

A highly stereoselective approach to the synthesis of functionalized pyran derivatives by Lewis acid assisted ketal reduction and allylation.

Reduction of bicyclic ketal 1 gave functionalized pyran derivatives 7a or 7b in a highly stereoselective manner, depending upon the reduction conditions utilized. For example, treatment of ketal 1 with TiCl4/Et3SiH produced exclusively diol 7b with the 2,5-syn relationship in good yield. Alternatively, reduction of ketal 1 by DIBALH gave 2,5-anti-diol 7a stereoselectively. Alane reductions of ketal 1 were highly stereoselective also; however, the syn/anti selectivity observed was strongly dependent on the ratio of reagents employed for in situ generation of the alane. Lewis acid catalyzed allylation of ketal 1 gave pyran 10 in a stereospecific alkylation reaction.

Synthesis of a 2,9-Dioxabicyclo[3.3.1]nonane via Double Intramolecular Hetero-Michael Addition: Entry to the F−G Ring System of the Azaspiracids

[structure: see text]. An effective approach to form a 1,3-disubstituted 2,9-dioxabicyclo[3.3.1]nonane system representing the core of the F and G rings (C28-C34) of the azaspiracid natural products has been developed. The double intramolecular hetero-Michael addition (DIHMA) of a diol upon an ynone generated the bicyclic ketal in a highly diastereoselective fashion.

ChemInform Abstract: Study on the Development of Catalyst Systems for the Novel Rearrangement Reaction of Bicyclic Ketal Compound (I).

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.

Study on the Development of Catalyst System for the Novel Rearrangement Reaction of Bicyclic Ketal Compound

A novel rearrangement of bicyclic ketals was investigated by using AcCl-NaI and MgBr2-Ac2O. Mono- and diacetylated products were isolated from these catalyst systems. Details of the chemistry are discussed.

Synthesis and NMR profiling of dioxabicyclo[3.2.1]octanes related to pinnatoxin D. Confirmation of the relative stereochemistry about rings E and F

Bicyclic ketals 3 and 4 were synthesised as models to confirm the proposed stereochemistry of the bicyclic ketal system (rings E,F) of the shellfish toxin pinnatoxin D. The key step is a stereoselective cyclisation of dihydroxyketones to provide the bicyclic structure.

Diastereoselective Formal Synthesis of the Antifungal Agent, (+)-Preussin. A New Entry to Chiral Pyrrolidines

A formal total synthesis of (+)-Preussin was achieved by using D-mannose as the starting material. The key step involved diastereoselective addition of allyltrimethylsilane to the bicyclic ketal 5. © 1997 Elsevier Science Ltd. All rights reserved.

ChemInform Abstract: Stereoselective Synthesis of Cyclic Ether Compounds via Reductive Cleavage of Bicyclic Ketals.

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.

The kinetics and thermodynamics of bicyclic ketal formation: An application to the synthesis of the zaragozic acids

The kinetics and thermodynamics of ketalization of tetrahydroxyketones are examined in the synthesis of the ketal core of zaragozic acid Bx3.

ChemInform Abstract: Selective, One‐Pot Synthesis of 2,3,6‐Trisubstituted Pyridine and 2‐ Cyclohexen‐1‐one Derivatives from Bicyclic Ketals.

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.

Anodically induced cycloaddition of vinylethylether to N-cyanomethyl-oxazolidine system. Stereoselective synthesis of β-amino ketal compounds

The anodic oxidation of N-cyanomethyloxazolidine system 1 initiates an electrocatalytic cycloaddition of vinylethylether at the N, O acetal function and affords, after NaBH 4 reduction and acid hydrolysis, the corresponding enantiomeric pure bicyclic ketal 4.

Stereoselective synthesis of cyclic ether compounds via reductive cleavage of bicyclic ketals

AbstractBicyclic ketals in the 6,8‐dioxabicyclo[3.2.1]octane system readily reacted with triethylsilane‐boron tri‐fluoride etherate at room temperature to give only the cis‐tetrahydropyranol derivatives via C5‐O6 bond cleavage. Three‐ and erythro‐alcohols were prepared selectively from the endo‐ and exo‐ketal, respectively. Dehydrated products also formed when the tertiary alcohol was involved under these reaction conditions. However, the cleavage reaction with aluminum hydride gave the trans‐tetrahydropyranol as the major product without dehydration.

Selective, one‐pot synthesis of 2,3,6‐trisubstituted pyridine and 2‐cyclohexen‐1‐one derivatives from bicyclic ketals

AbstractBoron difluoromethanesulfonate, prepared from 5 equivalents of trimethylsilyl methanesulfonate and 1 equivalent of boron trifluoride etherate, has proved to be an active Lewis acid catalyst for the one‐pot transformation reaction of bicyclic ketals in the 6,8‐dioxabicyclo[3.2.1]octane series to 2,3,6‐trisubstituted pyridine or 2‐cyclohexen‐1‐one selectively, depending on conditions. A 1,5‐diketone was the reaction intermediate for both products. Pyridine was formed selectively by using a nitrile as a solvent or a reagent, but cyclohexenone was prepared in methylene chloride instead of a nitrile.

ChemInform Abstract: Synthesis of Bicyclic Ketals Related to Zaragozic Acid by a Novel Photoannulation.

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.

Synthesis of bicyclic ketals related to zaragozic acid by a novel photoannulation

The 2,8-dioxabicyclo[3.2.1]octane ring system of the zaragozic acids was synthesized by a Norrish Type II photochemical reaction. This reaction occured through an unusual 1,6-hydrogen abstraction to generate a 1,5-biradical. A solvent study found that using benzene provides the best yield of the desired cyclized product.