Cycloaddition Of O-quinodimethane Research Articles

Stereoselective approach to potential scaffold of A-nor B-aromatic OSW-1 analogues via [4+2] cycloaddition of o-quinodimethane

A-nor B-aromatic steroidal skeleton was efficiently constructed by means of o-quinodimethane chemistry with exclusive stereoselectivity. The benzocyclobutene substrate for generation of the o-quinodimethane intermediate and subsequent [4+2] cycloaddition could be synthesized via (E)-selective Julia–Kocienski olefination and diastereoselective Grignard addition reactions. The synthesized tricyclic steroid-like compound with a trans-diol substructure would be utilized for divergent syntheses of potentially antitumor OSW-1 analogues with the truncated steroidal aglycone.

Thermodynamically stable [4 + 2] cycloadducts of lanthanum-encapsulated endohedral metallofullerenes.

The [4 + 2] cycloaddition of o-quinodimethanes, generated in situ from the sultine 4,5-benzo-3,6-dihydro-1,2-oxathiin 2-oxide and its derivative, to La metal-encapsulated fullerenes, La2@C80 or La@C82, afforded the novel derivatives of endohedral metallofullerenes (3a,b, 4a,b and 5b). Molecular structures of the resulting compounds were elucidated using spectroscopic methods such as MALDI–TOF mass, optical absorption, and NMR spectroscopy. The [4 + 2] adducts of La2@C80 (3a,b, and 4a,b) and La@C82 (5b), respectively, retain diamagnetic and paramagnetic properties, as confirmed by EPR spectroscopy. Dynamic NMR measurements of 4a at various temperatures demonstrated the boat-to-boat inversions of the addend. In addition, 5b revealed remarkable thermal stability in comparison with the reported [4 + 2] cycloadduct of pentamethylcyclopentadiene and La@C82 (6). These findings demonstrate the utility of sultines to afford thermodynamically stable endohedral metallofullerene derivatives for the use in material science.

ChemInform Abstract: Generation and Diels-Alder Reactions of N1-Substituted Pyrazole-4,5- quinodimethanes.

The cycloaddition of o-quinodimethanes (9-11) generated in situ from the 4,5-bisbromomethylpyrazole derivatives (6-8), with several dienophiles leads to the formation of the cycloadducts (12-20). These Diels-Alder reactions are also examined on the basis of some AM1 calculations

Studies toward Intramolecular Cycloaddition of o-Quinodimethane with an Oxazole Moiety

Thermal reaction of benzocyclobutene derivatives having an oxazole moiety was investigated. Intramolecular [4+2] cycloaddition of o-quinodimethane, generated by thermolysis of the benzocyclobutene, with the oxazole did not proceed, and instead, [1,5]-sigmatropic rearrangement occurred dominantly.

Intermolecular [4 + 2] Cycloaddition of o-Quinodimethanes Derived from Ene−Bis(sulfinylallenes)

Intermolecular [4 + 2] cycloaddition of o-quinodimethanes, prepared in situ from ene-bis(propargyl alcohols) and benzenesulfenyl chloride via ene-bis(sulfinylallene) formation, was investigated. Benzene-bridged bis(propargyl alcohols) reacted with both electron-deficient and electron-rich olefins to give the corresponding [4 + 2] cycloadducts. Ethylene-bridged bis(propargyl alcohols) underwent similar cycloaddition with electron-deficient olefins. Construction of some heterocycles based on the newly developed sequential reaction is also described.

TOTAL SYNTHESIS OF 11-AZASTEROIDS

ABSTRACT An efficient synthesis from readily available materials of 11-azasteroids is described. For the elaboration of the 11-aza structure, a pathway implying an intramolecular Diels-Alder cycloaddition of o-quinodimethanes is employed.

Generation and Diles-Alder Reactions of N1-Substituted Pyrazole-4,5-quinodimethanes

The cycloaddition of o-quinodimethanes (9-11) generated in situ from the 4,5-bisbromomethylpyrazole derivatives (6-8), with several dienophiles leads to the formation of the cycloadducts (12-20). These Diels-Alder reactions are also examined on the basis of some AM1 calculations

Synthesis of 1-Azabenzanthracene: Epimerization with the Use of 1,3-Dihydrobenzo(c)thiophene -S,S Dioxide as a Source ofortho-Quinodimethane

Abstract The cycloaddition of o-quinodimethane, from 1,3-dihydrobenzo(c)-S,S dioxide, to 5,6-dihydroquinoline yields a mixture of adducts isomeric at the newly created ring junction. The cycloadducts can be dehydrogenated to the fully aromatic 1-azabenzanthracene.

Tetra- and hexa-dehydroyohimbane synthesis by an intermolecular cycloaddition of o-quinodimethane

The thermolytic intermolecular cycloaddition reaction of 3,4-dihydro-β-carboline (9) with 1,2-dihydro-5-methoxy-benzocyclobutene-1-carbonitrile (6) gave 15,16,17,18,19,20-hexahydro-17-methoxy-yohimbane-14-carbonitrile (3) which was converted into the decyano-derivative (2) and tetradehydroyohimbane (12) by Birch reduction. Xylopinine (8) has been synthesised by a novel decyanation reaction, and 18-methoxyhexadehydro-yohimbane (4) has been obtained from 1-(1,2-dihydro-5-methoxybenzocyclobuten-1-yl)-3,4-dihydro-β-carboline (1).

Studies on the syntheses of tetracycline derivatives. I. Thermolytic cycloaddition of o-quinodimethanes with naphthoquinone.

Naphthoquinone (14) reacted with the o-quinodimethanes, which were generated from the benzocyclobutenes (9, 10 and 11), o-xylyl dibromide (12) and N-aminodihydroisoindole (13), to give the naphthacene-5, 12-quinones (15, 16, 17 and 18), respectively.