BC Ring Research Articles

Formation of the BC Ring System of Upenamide via a Staudinger/aza-Wittig Reaction

The BC ring system of upenamide was assembled using a stereoselective Diels-Alder reaction followed by a Staudinger/aza-Wittig/imine hydrolysis reaction. Stereoselective aldol coupling with an aldehyde that incorporates the DE ring system led to an advanced synthetic intermediate en route to the marine alkaloid upenamide.

Remarkable synthesis and structure of allene type zerumbone

The ring expansion of zerumbone to a 12-membered ring was studied via a ring opening system or a ring closure system of zerumbone. We succeeded in the synthesis of a zerumbone derivative with 12-membered ring, an allene type zerumbone. For the first time, a Doering–LaFlamme allene synthesis method was adopted and the structure was confirmed by monocrystal X-ray diffraction. It was obtained in total 27.7% yield from zerumbone. We believe that this compound is not only an important building block in synthesizing the BC ring of paclitaxel, but also plays an important role in a novel structure formation and a reactive discovery.

Synthetic studies toward the zoanthamine alkaloids: synthesis of the fully functionalized BC ring motif

A synthetic approach toward lactone 20 , representing the fully functionalized BC ring motif of the zoanthamine alkaloids, has been developed and is presented herein. The challenging C9 quaternary center of 20 was installed by a Wilkinson hydrogenation of enone 17 followed by construction of an α-bromo acetal and intramolecular cyclization exclusively from the α face of the BC ring system.

Stereoselective Synthesis of 19-Hydroxytaxoid by Utilizing Samarium(II) Iodide-Mediated Double Aldol Cyclization

Abstract The stereoselective synthesis of new 19-hydroxytaxoid 36, possessing a double-aldol skeleton was achieved by way of B to BC to ABC ring construction. Optically active 8-membered ring 6 corresponding to the B-ring of 19-hydroxytaxol has been synthesized in high yield from epoxyketo aldehyde 8 by intramolecular samarium(II) iodide-mediated double aldol cyclization. The bicyclic compound 5 corresponding to the BC ring system was prepared from the 8-membered ring 6 by successive trimethylaluminium-assisted stereoselective conjugated addition and intramolecular samarium(II) iodide-mediated double aldol cyclization. The ABC-ring system 4 was constructed by stereoselective homoallylation and pinacol coupling cyclization with low-valent titanium. The synthesis of new 19-hydroxytaxoid 36 was accomplished from ABC ring system 4 by olefination of vicinal diol unit.

Synthetic Approaches to Guanacastepenes. Enantiospecific Syntheses of BC and AB Ring Systems of Guanacastepenes and Rameswaralide.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthetic approaches to guanacastepenes. Enantiospecific syntheses of BC and AB ring systems of guanacastepenes and rameswaralide.

[reaction: see text] A simple and efficient approach for the BC and AB ring systems of the novel diterpenes guanacastepenes and rameswaralide starting from the readily and abundantly available monoterpene (R)-carvone employing RCM reaction as the key step is described.

A Short Synthesis of (+)‐Narciclasine via a Strategy Derived from Stereocontrolled Epoxide Formation and SnCl4‐Catalyzed Arene‐Epoxide Coupling.

A facile construction of the typical framework of narcissus alkaloids has been realized by virtue of the development of a practical route involving stereocontrolled epoxide formation and SnCl(4)-catalyzed arene-epoxide coupling. To achieve this goal, it proved to be necessary to devise a strategy that would enable chemical transformations to install an epoxy moiety in a congested environment. The successful preparation of a hindered epoxide from O-isopropylidene-protected 4-aminocyclohexenol required three steps consisting principally of controlled bromohydration and base-promoted closure and N-alkylation. It was found that a catalytic amount of SnCl(4) not only maintained the catalytic cycle but also effected clean arylation to form a fused BC ring system. Several tactics that ultimately proved to be unsatisfactory are also discussed in an effort to set important boundary limits on arene-epoxide coupling. The requisite enantiopure 4-aminocyclohexenol was available via an asymmetric cycloaddition of diene to camphor-based chloronitroso. The total synthesis of (+)-narciclasine was realized in nine steps with an overall yield of 19%.

Towards a Total Synthesis of Guanacastepene A: Construction of Fully Functionalized AB and BC Ring Segments.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Rearrangement Pathways in the Bicyclo[4.4.1]undecane Ring System.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A short synthesis of (+)-narciclasine via a strategy derived from stereocontrolled epoxide formation and SnCl(4)-catalyzed arene-epoxide coupling.

A facile construction of the typical framework of narcissus alkaloids has been realized by virtue of the development of a practical route involving stereocontrolled epoxide formation and SnCl(4)-catalyzed arene-epoxide coupling. To achieve this goal, it proved to be necessary to devise a strategy that would enable chemical transformations to install an epoxy moiety in a congested environment. The successful preparation of a hindered epoxide from O-isopropylidene-protected 4-aminocyclohexenol required three steps consisting principally of controlled bromohydration and base-promoted closure and N-alkylation. It was found that a catalytic amount of SnCl(4) not only maintained the catalytic cycle but also effected clean arylation to form a fused BC ring system. Several tactics that ultimately proved to be unsatisfactory are also discussed in an effort to set important boundary limits on arene-epoxide coupling. The requisite enantiopure 4-aminocyclohexenol was available via an asymmetric cycloaddition of diene to camphor-based chloronitroso. The total synthesis of (+)-narciclasine was realized in nine steps with an overall yield of 19%.

Towards a total synthesis of guanacastepene A: construction of fully functionalized AB and BC ring segments

Studies directed towards the total synthesis of the diterpene antibiotic, guanacastepene A, of current interest and displaying promising biological activity against drug-resistant pathogens, has led to the acquisition of fully functionalized AB and BC ring segments of the natural product.

Rearrangement pathways in the bicyclo[4.4.1]undecane ring system

The readily available bicyclo[4.4.1]undecane ring system can be transformed into the isomeric bicyclo[5.3.1]undecane and bicyclo[5.4.0]undecane systems via related rearrangement pathways. The resultant products constitute the AB ring substructure of the taxane diterpenes and the BC ring substructure of the tigliane diterpenes, respectively.

Preparation of the 14-membered l, l-cycloisodityrosine subunit of RP 66453

The synthesis of the reversed 14-membered l, l-cycloisodityrosine 9 constituting an appropriately functionalized BC ring system of RP 66453 is detailed.

Progress toward the Total Synthesis of Ingenol: Construction of the Complete Carbocyclic Skeleton

[reaction: see text] The complete carbocyclic skeleton of ingenol is assembled via a route that employs ring-closing metathesis (RCM) to close the strained "inside-outside" BC ring system (i.e., 24 --> 25).

A novel approach to the taxane BC ring system through formation of alpha-ketol by oxidative removal of the phenylsulfonyl group with subsequent in situ oxidation.

Cis-fused bicyclo[6.4.0]dodecene 11 was converted into taxane BC ring system 21 in three steps; transformation of the phenylsulfonyl group to an alpha-hydroxy carbonyl group by the treatment with potassium hexamethyldisilazide (KHMDS) and triethyl phosphite under oxygen atmosphere, followed by reductive elimination of the hydroxyl group of alpha-ketol moiety, and inversion of ring juncture. Epimerization of the sulfonyl group of 11 was indispensable for the first oxidation process (17 --> 18) and the second oxidation of 12 leading to hydroxylation at the alpha-position of the carbonyl group proceeded with high regio- and stereoselectivity to give 13. On the other hand, reaction of the cross-conjugated compound 5 with KHMDS at 0 degrees C brought about a complete reorganization of molecular framework to provide the compound 7 in which the five-membered ring and the conjugated seven-membered ring were connected through a single bond.

Synthesis of 18-Demethyltaxoid via Stereoselective Allylation and Intramolecular Aldol Condensation Reactions

Abstract Optically active novel 18-demethyltaxiods were successfully synthesized from 2α,10β-dibenzyloxy-11β-(t-butyldimethylsiloxy)-7β-hydroxy-1α-(p-methoxybenzyloxy)-8β,15,15-trimethyl-4-methylene-trans-bicyclo[6.4.0]dodecan-9-one (2) which corresponds to the BC ring system of Taxol by stereoselective allylation and intramolecular aldol condensation reactions.

Diethylaluminum Ethoxide Mediated Stereoselective Diels-Alder Reaction of α,β-unsaturated Ketones and Acetoxy-1,3-butadienes as Diene Components

Abstract Stereoselective Diels-Alder reaction between several α,β-unsaturated ketones and acetoxy-1,3-butadienes is effectively performed by the promotion of diethylaluminum ethoxide under mild conditions. This reaction is successfully applied to the synthesis of optically active bicyclo[6.4.0]dodecanone 9 which corresponds to the BC ring system of 10-deoxy taxane derivatives from the 8-membered ring enone 7 and diene 2.

Synthesis of the tetracyclic ABCE ring subunit I, bearing the 13-membered azacycle, of manzamine A

The tetracyclic ABCE ring, which bears the crucial 13-membered azacycle, of manzamine A has been synthesized through the corresponding bicyclic BC ring subunit as a promising synthetic intermediate.

ChemInform Abstract: Stereocontrolled Synthesis of the BC Ring System of Taxol.

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 New Method for the Synthesis of Baccatin III

Abstract Baccatin III was efficiently synthesized from the BC ring system of Taxol,2α,10β-dibenzyloxy-11β-(t-butyldimethylsil-oxy)-7β-hydroxy-1α-(4-methoxybenzyloxy)-8β,15,15-trimethyl-4-methylene-trans-bicyclo[6.4.0]dodecan-9-one(1), by succes-sive constructions of A and D rings via respective intramolecular pinacol coupling and oxetane forming reaction.