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Relevant academic research and scientific papers

A concise synthesis of (-)-aplyviolene facilitated by a strategic tertiary radical conjugate addition

A second-generation synthesis of the rearranged spongian diterpene aplyviolene is reported. The key step is the addition of a trialkyl tertiary radical generated by photoredox-mediated fragmentation of a N-(acyloxy) phthalimide to an α-chloropentenone (se

A concise synthesis of (-)-aplyviolene facilitated by a strategic tertiary radical conjugate addition

A second-generation synthesis of the rearranged spongian diterpene aplyviolene is reported. The key step is the addition of a trialkyl tertiary radical generated by photoredox-mediated fragmentation of a N-(acyloxy) phthalimide to an α-chloropentenone (se

Synthesis of the proposed structure of mucoxin via regio- and stereoselective tetrahydrofuran ring-forming strategies

An enantioselective total synthesis of the proposed structure of mucoxin (1) is described. Mucoxin, an annonaceous acetogenin isolated from bioactive leaf extracts of Rollinia mucosa, is the first acetogenin containing a hydroxylated trisubstituted tetrah

Total syntheses of (+)-australine and (-)-7-epialexine

Three approaches were examined for the synthesis of 3-(hydroxymethyl)pyrrolizidines, a class of compounds that includes the polyhydroxylated pyrrolizidine alkaloids alexine (1), australine (2), and various stereoisomers of thereof. In the first approach, the intramolecular cycloaddition of an azide onto an electron-rich 1,3-diene bearing a terminal alkoxymethyl substituent (i.e., 21) afforded the dehydropyrrolizidines 22a and 22b, with 22a predominating. A rationale for this stereoselectivity was proposed. Transformation of the major diastereomer 22a into a natural 3-(hydroxymethyl)-pyrrolizidine was not possible due to difficulties encountered in transforming the phenyl vinyl sulfide functionality into other useful functional groups. A second approach was examined, Wherein the intramolecular cycloaddition of an azide with an optically pure S-t-Bu-substituted diene (i.e., 30) was found to produce the pyrrolizidine 31. In this case, the alkoxymethyl substituent was incorporated into the tether between the azide and the diene, rather than on the diene itself. A key transformation in the synthesis of the diene 30 was the use of the allylic borane R2BCH2CH=C(TMS)(StBu) for the stereoselective conversion of the D-arabinose-derived azido aldehyde 28 to the E-isomer of 30. The cyclization of 30 to 31 also produced the bicyclic triazene 32, the result of 1,3-dipolar cycloaddition of the azide onto the distal double bond of the diene. Again, difficulties in transformation of the vinyl sulfide functionality of 31 into useful oxygen functionality limited this approach to naturally occurring 3-(hydroxymethyl)pyrrolizidines. A third approach to these compounds was successful. The transformation of L-xylose into the azido epoxy tosylate 46 was accomplished using two Wittig reactions and an epoxidation, in addition to other standard functional group manipulations. Reductive double-cyclization of 46 afforded the pyrrolizidines 47a and 47b, which were debenzylated to afford (+)-australine 2 and (-)-7-epialexine 4, respectively. In the preliminary report of this work, erroneous spectroscopic data in the original literature on the structural assignment of australine led to the conclusion that the synthetic material obtained herein was actually (+)-7-epiaustraline. Recently corrected spectroscopic data have appeared which verify that (+)-australine 2 was indeed synthesized for the first time.

Samarium(II) iodide-mediated reductive annulations of ketones bearing a distal vinyl epoxide moiety

Samarium(II) iodide in the presence of hexamethylphosphoramide (HMPA) efficiently promotes the intramolecular coupling of ketones with distal epoxy olefins. The reaction appears to proceed by a mechanism wherein a ketyl couples with the unsaturated epoxide. Subsequent fragmentation of the epoxide ring in compounds 1a-k yields carbocycles 2a-k with an allyl alcohol side chain in good yields, and often with high diastereoselectivity. When tetramethylguanidine was used as an additive instead of HMPA, the desired carbocycle was obtained in good yield, but the diastereoselectivity was diminished. A palladium(0)-catalyzed SmI2 reaction provided the expected product in modest yield, but the sense of diastereoselectivity was reversed. In the latter case, a different reaction mechanism may be involved. Thus, formation of an allylsamarium species may be invoked, with nucleophilic carbonyl addition leading to the observed facial selectivity.

Synthesis of (-)-Slaframine and Related Indolizidines

An enantioselective synthesis of the indolizidine alkaloid (-)-slaframine 1 is reported.Reductive double cyclization of the azido epoxy tosylate 48 afforded the indolizidine 52, which was converted to (-)-slaframine in two steps.The cyclization substrate

A Synthesis of (-)-Slaframine and (-)-1,8a-Diepislaframine

Reductive cyclization of the optically pure azido epoxides 12 and 13 afforded the indolizidines 14 and 16, which were converted into (-)-slaframine 1 and (-)-1,8a-diepislaframine 18.

PALLADIUM-CATALYZED STEREOCONTROLLED CYCLIZATION OF 1,3-DIENE MONOEPOXIDE: A ROUTE TO A NEW SYNTHETIC INTERMEDIATE FOR DE-AB-CHOLESTANE DERIVATIVE.

The optically active (2R,3R)-3--2-(3-butenyl)-2-methyl-1-cyclopentanone (8) was synthesized as a precursor of vitamin D3 (5) by palladium-catalyzed syn-SN2' cyclization of -