Ruthenium Porphyrin Catalyzed Tandem Sulfonium/Ammonium Ylide Formation and [2,3]-Sigmatropic Rearrangement. A Concise Synthesis of (±)-Platynecine
作者:Cong-Ying Zhou、Wing-Yiu Yu、Philip Wai Hong Chan、Chi-Ming Che
DOI:10.1021/jo049540v
日期:2004.10.1
allyl sulfides such as crotyl sulfide produced an equimolar mixture of anti- and syn-2-(ethylthio)-3-methyl-4-pentenoic acidethyl ester. The analogous “EDA + N,N-dimethylcrotylamine” reaction afforded a mixture of anti- and syn-2-(N,N-dimethylamino)-3-methyl-4-pentenoic acidethyl esters with a diastereoselectivity of 3:1. The observed catalytic activity of [RuII(TTP)(CO)] for the ylide [2,3]-sigmatropic
A stereocontrolled route to both enantiomers of the necine base dihydroxyheliotridane via intramolecular 1,3-dipolar addition using the same chiral precursor
Diastereofacialselectivity in an enantiospecific intramolecular 1,3-dipolar addition is controlled by adjusting the size of the tether between the dipole and the dipolarophile to give 2,3-disubstituted pyrrolidines enantiomeric with respect to the newly generated stereogenic 2,3-centres depending on the tether size; this leads to Stereocontrolledsynthesis of both enantiomers of the necine base d
Synthesis of Indolizidines and Pyrrolizidines through the [2 + 2]Cycloaddition of Five-Membered Endocyclic Enecarbamates to Alkyl Ketenes. Unusual Regioselectivity of Baeyer−Villiger Ring Expansions of Alkyl Aza-Bicyclic Cyclobutanones
作者:Antonio R. de Faria、Elias L. Salvador、Carlos Roque D. Correia
DOI:10.1021/jo016189u
日期:2002.5.1
regioisomeric lactones in a ratio of approximately 1.5 to 1. It is hypothesized that the steric strain built into the Criegee cyclobutane intermediate is the regioselective controlling factor in these oxidations, overriding any stereoelectronic bias for ringexpansion. A rationale for the mechanism of the [2 + 2]cycloaddition involving enecarbamates and ketenes is presented, which seems to involve the participation
Necine bases of pyrrolizidine alkaloids, turneforcidine, hastanecine, and platynecine are synthesized from ethyl 1-hydroxy-2,3,5,6-tetrahydro-1H-pyrrolizine-7-carboxylate in racemic form.
Ring Expansion of Azetidinium Ylides: Rapid Access to the Pyrrolizidine Alkaloids Turneforcidine and Platynecine
作者:John A. Vanecko、F. G. West
DOI:10.1021/ol050915o
日期:2005.7.1
Azetidinecarboxylate esters react readily with metallocarbenes in an inter- or intramolecular fashion to generate azetidinium ylides. Efficient [1,2]-shift by the ester-substituted carbon furnishes ring-expanded pyrrolidine products. In the case of substrate 1, this provides access to the pyrrolizidine alkaloids turneforcidine and platynecine via a high-yield, five-step sequence starting with readily available methyl 1-benzylazetidine-2-carboxylate.