177979-77-0Relevant academic research and scientific papers
Alkenyl nitrones cyclizations induced by phenylselenenyl bromide. A convenient synthetic route to 1,2-oxazines
Tiecco, Marcello,Testaferri, Lorenzo,Bagnoli, Luana
, p. 6811 - 6822 (2007/10/03)
Alkenyl nitrones reacted with phenylselenenyl bromide to afford ring closure reaction products deriving by the intramolecular capture of the seleniranium intermediates by the oxygen atom. Owing to the relative positions of the oxygen atom and of the carbon-carbon double bond in the nitrones employed, six-membered cyclic iminium salts were thus formed. These have been directly treated with nucleophilic reagents and afforded 1,2-oxazine derivatives in good yield. It has been observed that, under the experimental conditions employed, the iminium salts in which the carbon-nitrogen double bond is exocyclic, depending on the nucleophile employed, gave the N-alkyl 1,2-oxazines and/or the N-unsubstituted 1,2-oxazines. On the contrary, with iminium salts in which the carbon-nitrogen double bond is endocyclic only N-alkyl 1,2-oxazines were obtained.
Stereospecific Synthesis of 2,3,6-Trisubstituted Piperidines: An Efficient Total Synthesis of (+/-)-Pumiliotoxin C
LeBel, Norman A.,Balasubramanian, N.
, p. 3363 - 3368 (2007/10/02)
The intramolecular cycloaddition of N-(1-alkyl-4-pentenyl)nitrones provides a highly regio- and stereoselective route to all-cis-2,6-disubstituted-3-(hydroxymethyl)piperidines 3 by way of the bicyclic isoxazolidines 2.In demonstration studies, the 2,6-dimethyl analogue was transformed into 2r,3c,6c-trimethylpiperidine (9) and into N-tert-butoxy-2c,6c-dimethylpiperidine-3r-carboxaldehyde (10).Facile and complete epimerization of the latter into the all-equatorial, 2t,3r,6t aldehyde 11 was achieved, thus giving entry into the diastereomeric 2,3,6-trisubstitutedpiperidines.These protocols can give rise to short and efficient syntheses not only of the piperidines but of bicyclic nitrogen heterocycles depending on the nature of the substituents.An additional stereogenic center was introduced into the 3-(1-hydroxyalkyl) side chain by employing trans and cis isomers of N-(1,5-disubstituted-4-pentenyl)nitrones.The methodology was used to rapidly assemble a piperidine containing four stereogenic centers starting from 2-pentanone and methyl phenyl ketone.This intermediate 20 was then easily converted into (+/-)-pumiliotoxin C (12) by way of an intramolecular alkylation with inversion of configuration.The highly convergent total synthesis was accomplished in 14 steps and 14percent overall yield with no attempt at optimization.
