“…The transition-state model TS-4 was suggested to involve a s - cis configuration of the dipolarophile with union occurring between the re face of the menthyl acrylate and the si face of the dipole, as the carbonyl group of the ester is syn -planar with the menthyl C(1)−H and the si face of the acrylate is effectively shielded by the C(2) i -Pr group. The same group further reported the cycloaddition of nonmetalated 195 as well as metalated azomethine ylide 196 , derived from diazepine-1-carboxylate derivatives 194 , to the N -methylmaleimide and ethyl acrylate, respectively, to obtain corresponding spiro-cycloadducts 197 and 198 in a complete regio- and stereoselective manner and in excellent chemical yields (84−93%, Scheme ). More recently, this group also studied in detail the cycloaddition of uracil polyoxin-derived azomethine ylides 200 and 201 with various maleimides, and the results are summarized in Scheme .…”
“…The transition-state model TS-4 was suggested to involve a s - cis configuration of the dipolarophile with union occurring between the re face of the menthyl acrylate and the si face of the dipole, as the carbonyl group of the ester is syn -planar with the menthyl C(1)−H and the si face of the acrylate is effectively shielded by the C(2) i -Pr group. The same group further reported the cycloaddition of nonmetalated 195 as well as metalated azomethine ylide 196 , derived from diazepine-1-carboxylate derivatives 194 , to the N -methylmaleimide and ethyl acrylate, respectively, to obtain corresponding spiro-cycloadducts 197 and 198 in a complete regio- and stereoselective manner and in excellent chemical yields (84−93%, Scheme ). More recently, this group also studied in detail the cycloaddition of uracil polyoxin-derived azomethine ylides 200 and 201 with various maleimides, and the results are summarized in Scheme .…”
“…Further examples for cycloadditions are presented by Grigg and co-workers . Starting from the corresponding imines, the authors react ( R )-menthyloxy furanone 4a in the presence of DBU to receive complex cyclic systems 45 (see Scheme ).…”
Section: 15 13-dipolar Cycloadditionsmentioning
confidence: 99%
“…Starting from the corresponding imines, the authors react ( R )-menthyloxy furanone 4a in the presence of DBU to receive complex cyclic systems 45 (see Scheme ). 20 Cycloaddition Products According to Grigg et al …”
Scheme 4. Synthesis of a Kuehneromycin A and Mniopetal Precursor According to Jauch 11 Scheme 5. Diels-Alder Reaction of o-Quinonoid Pyrone 12 Scheme 6. Synthesis of C-Ring Fragment of Cobyric Acid Scheme 7. Starting Sequence of the Cyanobacterin Synthesis by Ishibashi et al. 15
“…The reaction under microwaves is substantially faster and the yield is nearly quantitative after 15 min. The classical reaction (even with the recommended catalyst [16]) gave only a 44% yield after 18 h. As for the stereoselectivity, it was lower in the classical case. This effect might be partially due to the effect of the lithium used, which is known for its complexing ability.…”
New compounds with the ethyl hexahydro-1H-pyrrolo[3,2-c]quinoline-2-carboxylate skeleton were prepared by microwave-assisted intramolecular 1,3-dipolar cycloaddition reactions. The reactions were carried out under solvent-free conditions and compared with the same reaction in the presence of a solvent and a catalyst. Steric effects on the selectivity of the reaction were noted and evaluated.
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