159682-50-5Relevant academic research and scientific papers
Application of cross-conjugated heteroaromatic betaines to the synthesis of the schizozygane alkaloid (±)-strempeliopine
Bobeck, Drew R.,Hyoung, Ik Lee,Flick, Andrew C.,Padwa, Albert
experimental part, p. 7389 - 7402 (2010/02/17)
(Chemical Equation Presented) An efficient stereocontrolled route to the isoschizozygane alkaloid core has been developed utilizing an intramolecular 1,4-dipolar cycloaddition of a cross-conjugated heteroaromatic betaine. The resulting cycloadduct undergo
An approach to the isoschizozygane alkaloid core using a 1,4-dipolar cycloaddition of a cross-conjugated heteroaromatic betaine
Padwa, Albert,Flick, Andrew C.,Hyoung, Ik Lee
, p. 2925 - 2928 (2007/10/03)
(Chemical Equation Presented) A new strategy for the synthesis of the isoschizozygane alkaloid core has been developed that is based on a 1,4-dipolar cycloaddition reaction of a cross-conjugated heteroaromatic betaine. The resulting cycloadduct undergoes
Cycloaddition Reaction of Mesoionic Betaines as an Approach toward Trialkylindoline Alkaloids
Padwa, Albert,Harring, Scott R.,Semones, Mark A.
, p. 44 - 54 (2007/10/03)
Intramolecular 1,4-dipolar cycloaddition of an anhydro-4-hydroxy-2-oxo-1,3-thiazium hydroxide across a tethered indole π-bond has been used for the construction of the pentacyclic skeleton of epi-16,17-dihydroeburnamenine. The reaction of 3-ethyl-3-(alkenyl)piperidinones with diketene and trimethylsilyl triflate in benzene at ambient temperature produced annulated pyridones in good yield. The initial reaction involved formation of a N-acetoacetylated amide which was further converted to the pyridone with TMSOTf. The overall process was found to proceed with complete stereospecificity. Treating a sample of 3-ethyl-3-[(E)-4-phenyl-3-butenyl]-2-piperidone with diketene and TMSOTf produced a cycloadduct in 63% yield whose stereochemistry was elucidated by a X-ray crystallographic study. The epimeric Z-isomer produced a different stereoisomer of the annulated dihydropyridone. The mechanism of the annulation involves a TMSOTf induced cyclization followed by proton removal and generation of a cross-conjugated heteroaromatic betaine. This 1,4-dipole undergoes a subsequent intramolecular dipolar cycloaddition across the neighboring π-bond, and the resulting cycloadduct is subsequently converted to the annulated lactam. A related annulation sequence leading to a key intermediate previously utilized in the synthesis of the (±)-vallesamidine has been developed which is based on the intramolecular dipolar cycloaddition of a mesoionic betaine intermediate.
On the intramolecular 1,4-dipolar cycloaddition reaction of thiazinium betaines for the construction of aza-, diaza-, and polyaza-heterocyclic ring systems
Padwa,Coats,Harring,Hadjiarapoglou,Semones
, p. 973 - 984 (2007/10/02)
A series of bicyclic anhydro-4-hydroxy-2-oxo-1,3-thiazinium hydroxides containing tethered π-systems are easily prepared from the reaction of thiolactams with 1,3-bielectrophiles. These cross-conjugated heteroaromatic betaines undergo regio- and stereospecific 1,4-dipolar cycloaddition in good yield to produce cycloadducts containing a carbonyl sulfide bridge which can be induced to lose COS on further heating. Two of the cycloadducts were characterized by single crystal X-ray determinations. Control of ring size in the final product of the cycloaddition can be achieved by variation of the dipolarophilic chain length. Entry to the [6,6,5]- and [6,6,6]pyridone ring systems was possible using phenylalkynyl-substituted thioamides. Intramolecular 1,4-dipolar cycloaddition of a thiazinium betaine dipole also occurs across an indolyl π-bond. With only one substituent group in the 9-position of the bicylic betaine, the reaction takes an entirely different course unless a highly activated π-bond is incorporated into the tether. The preferred reaction with modestly activated π-systems corresponds to loss of the activated proton to produce an S,N-ketene acetal. When a ketene S,S-acetal group was incorporated onto the side chain, the 1,4-dipolar cycloaddition reaction was facilitated relative to proton loss.
Cycloaddition chemistry of anhydro-4-hydroxy-1,3-thiazolium hydroxides (thioisomunchnones) for the synthesis of heterocycles
Padwa,Harring,Hertzog,Nadler
, p. 993 - 1004 (2007/10/02)
A series of α,α-disubstituted thioisomunchnones were prepared by treating acyclic or cyclic thioamides with bromoacetyl chloride in the presence of triethylamine. The resulting mesoionic dipole was found to undergo bimolecular 1,3-dipolar cycloaddition wi
