[4+2]-Cycloaddition of 3,6-bis(3,5-dimethyl-4-R-pyrazol-1-yl)-1,2,4,5-tetrazines with alkenes

A number of 1,4-dihydropyridazines and pyridazines were prepared by the Diels-Alder reaction with an inverse electron demand from cyclic heterodiene systems, 3,6-bis(3,5-dimethyl-4-R-pyrazol-1-yl)-1,2,4,5-tetrazines, and some enamines as well as from 4-vinylpyridine, butyl vinyl ether, phenylacetylene, and acrylamide. The reaction of 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2,4,5-tetrazine with styrene afforded 4,5-dihydropyridazine, which was readily oxidized by atmospheric oxygen to form the corresponding pyridazine. Electron-withdrawing substituents (Br or Cl) in the pyrazole rings accelerate [4+2]-cycloaddition. When heated, 1,4-dihydropyridazines, which were synthesized from tetrazines and enamines, eliminated amine to give pyridazines. The reactivities of tetrazines were evaluated by quantum-chemical methods. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 354–360, February, 2000.     

[4+2] Cycloaddition of 1-phosphono-1,3-butadiene with azo- and nitroso-heterodienophiles

Under microwave activation, diethyl 1-phosphono-1,3-butadiene (1) reacted with t-butyl azodicarboxylate (2) and o-nitrosotoluene (5) to furnish quantitatively [4+2] cycloadducts, 3-phosphono-3,6-dihydro-1,2-pyridazine (3) and 6-phosphono-3,6-dihydro-1,2-oxazine (6), respectively. Selective oxidation and/or reduction of 6 led to functionalized δ-aminophosphonic derivatives in cyclic (7, 8) and aliphatic series (9, 10). Intermediate 10 may be cyclized into 2-phosphono-2,5-dihydro-1-pyrrole (12).     

Diastereoselective synthesis of β-aminocyclopentene sulfonic acid via hetero Diels-Alder reaction

A new cyclopentene GABA analogue was synthesized as a conformationally rigid analogue of the epilepsy drug vigabatrin. N-Sulfinyl dienophile Diels-Alder methodology, followed by alkaline hydrolysis of the corresponding dihydrothiazine oxide, oxidation and deprotection of the amino group gave cis-4-aminocyclopent-2-ene-1-sulfonic acid. The corresponding N,N-dimethylsulfinamide was also obtained.     

Stereoselective Synthesis of the Decahydrofluorene Core of the Hirsutellones

A stereoselective synthesis of the decahydrofluorene core of the hirsutellones was accomplished in eight steps and in 43% overall yield. The key step of the synthesis is the highly stereoselective intramolecular Diels-Alder cyclization of the siloxacyclopentene-constrained tetraene 1.     

Synthetic studies on the dienophile unit of methyl isosartortuoate. Part 1: Assembly of the acyclic precursor

A strategically functionalized compound, as the acyclic precursor of the dienophile unit of methyl isosartortuoate has been synthesized, and its stereochemistry was also assigned.     

Total Synthesis of (−)-Lepadin F based on a Stereoselective Diels–Alder Reaction Controlled by a Ketolactone-type Dienophile

An efficient approach to the type III lepadin alkaloids (lepadins F and G) has been developed through a key Diels–Alder reaction, in which a novel ketolactone-type dienophile with chiral diol unit is employed to generate the desirable all-cis-trisubstituted cyclohexene with excellent regio- and stereoselectivity control. The subsequent selective sulfonylation of the diol unit followed by S_N2 cyclization under hydrogenation conditions could construct the substituted piperidine ring. By using this approach, (−)-lepadin F is synthesized from ethyl l -lactate for the first time.     

Synthetic studies on the dienophile unit of methyl isosartortuoate. Part 2: SmI2-mediated 14-membered carbocyclization

The dienophile unit of methyl isosartortuoate has been synthesized. The 14-membered carbocycle was constructed by a SmI₂-mediated intramolecular Reformatsky reaction. The introduction of the oxo group at the γ-position of the α,β-unsaturated ester was achieved by rearrangement of an β,γ-epoxy ester.     

Reactions of acceptor thiophene 1,1-dioxides with dienes. Synthesis of bisadducts

Cycloaddition of dienes to thiophene dioxides affords mono-and bisadducts, depending on the reaction conditions. Regio-and stereochemical specific features of the cycloaddition were revealed. The thermal rearrangement of the monoadduct was found. Dedicated to Academician N. S. Zefirov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2117–2121, September, 2005.     

亚胺的杂Diels-Alder反应在天然产物合成中的应用

综述了近年来用亚胺杂Diels-AJder反应合成天然产物的研究进展．