1730-25-2Relevant articles and documents
Electronic Control of Stereoselectivity. 11. Long-Range Modulation of Stereoselection in Diels-Alder Cycloadditions of N-Methyltriazolinedione to Aryl-Substituted 9-Butadienylidenebenzonorbornenes
Paquette, Leo A.,Klinger, Francois
, p. 272 - 275 (1982)
Three 9-butadienylidenebenzonorbornenes (4a-c) have been synthesized and their ability to enter into Diels-Alder reaction examined.Although these substances are unreactive to a host of dienophiles, tetracyanoethylene enters into addition with 4b and 4c.However, these reactions do not allow for examination of the stereoselectivity question.When recourse was made to the more reactive N-methyltriazolinedione reagent, adducts 9 and 10 were produced in the following syn/anti ratios: 4a, 49:51; 4b, 24:76; 4c, 24:76.The chemical shifts of the N-methyl groups in the urazole segments of these adducts proved quite divergent and conducive to reliable structural assignment.The results are interpreted in terms of zwitterion intervention, with charge delocalization into the aromatic ring where this is feasible (the tetrafluoro example excluded).Because of this long-range homoaromatic stabilization, closure of the second C-N bond from the anti direction is kinetically favored.
Characterization of typical potent odorants in raw and cooked Toona sinensis (A. Juss.) M. Roem. by instrumental-sensory analysis techniques
Yang, Wenxi,Cadwallader, Keith R.,Liu, Yuping,Huang, Mingquan,Sun, Baoguo
, p. 153 - 163 (2019/01/26)
Toona sinensis (A. Juss.) M. Roem. (TS) possesses a unique and pleasant flavor and is consumed as a popular seasonal vegetable in certain parts of eastern and southeastern Asia. The potent odorants in raw and cooked TS were identified by combined sensory and instrumental analysis techniques, including sensory descriptive aroma profiling and two complimentary volatile isolation methods combined with gas chromatography-olfactometry (GC-O) techniques. Highly volatile odorants were determined by static headspace dilution analysis (SHDA)-GC-O, while those of intermediate- and semi-volatility were determined by solvent-assisted flavor evaporation-aroma extract dilution analysis (SAFE-AEDA). Among the numerous odorants identified by SHDA and SAFE-AEDA, (E,E)-bis-(1-propenyl) disulfide was found to be predominant in both raw and cooked TS. In agreement with results of sensory descriptive analysis, hexanal, (Z)-3-hexenal, (E)-2-hexenal and (Z)-3-hexen-1-ol contributed green, grassy and leafy aroma notes; while hydrogen sulfide, methyl thiirane, (E,E)-bis-(1-propenyl) disulfide and (E,Z)-bis-(1-propenyl) disulfide contributed pungent, sulfurous and alliaceous notes in TS.
Dynamic kinetic asymmetric cross-benzoin additions of β-stereogenic α-keto esters
Goodman, C. Guy,Johnson, Jeffrey S.
supporting information, p. 14698 - 14701 (2014/12/11)
The dynamic kinetic resolution of β-halo α-keto esters via an asymmetric cross-benzoin reaction is described. A chiral N-heterocyclic carbene catalyzes the umpolung addition of aldehydes to racemic α-keto esters. The resulting fully substituted β-halo glycolic ester products are obtained with high levels of enantio- and diastereocontrol. The high chemoselectivity observed is a result of greater electrophilicity of the α-keto ester toward the Breslow intermediate. The reaction products are shown to undergo highly diastereoselective substrate-controlled reduction to give highly functionalized stereotriads.
