Diels‐Alder ‐Reaktionen von 2′‐substituierten 3‐Vinyl‐1 H ‐indolen zu neuen anellierten Indol‐und Carbazol‐Derivaten

Eitel

1988

Self Cite

Dedicated to Prof. Dr. h. c. mult. H . Bohme (Marburg, FRG) with the best wishes for his 80th birthday (17.111.88) By means of an intramolecular Wittig process, 2-vinylindole (2) was prepared. The indole 2 functions as a heterocyclic, donor-activated 1,3-diene and undergoes [4 + 21 cycloaddition reactions with dimethyl acetylenedicarboxylate, N-phenylmaleimide, and p-benzoquinone leading to the novel carbazole derivatives 3,4,5c, 6, and 7, respectively. The reaction of 2 with acceptor(A)-substituted dienophiles (e.g. ACH=CH2, A C X H ) does not yield products that can be isolated.Vinylindoles are able to take part in various cycloaddition processes, e.g. Diels-Alder reactions. In these transformations, the vinylindoles may react both as dienes and as dienophiles. In this way, they have been used by us and by others in several syntheses of heterocyclic compounds and alkaloids [ 1-61. Up till now, mostly selectively functionalized vinylindoles have been the reaction partners since as a consequence of stability factors [3] [7], these compounds are more easily accessible in higher yields than the parents.Of the series of parent vinylindole compounds, only 3-vinylindole has been prepared previously by means of a Cope elimination from N,N-dimethyltryptamine N-oxide, and its Diels-Alder reactions were only superficially investigated [8]. In the present publication, we report on the first synthesis of the parent 2-vinylindole (2) and its cycloadditions with dienophiles.The 2-vinylindole (2) is prepared without difficulty in 38% yield from (2-aminobenzy1)triphenylphosphonium bromide (la) as starting material via l b by way of an intramolecular Wittig process according to Le Corre's method [9] (Scheme I). The thermally stable, crystalline vinylindole 2 functions as a 4z-component in [4 + 21 cycloadditions with symmetrical carbodienophiles. Under reflux conditions in absolute toluene, reactions of 2 with the dienophiles tested by us, namely dimethyl acetylenedicarboxylate and N-phenylmaleimide, give rise to the carbazole derivatives 3 and 4, ') Part V1 in the series 'Cycloadditions of Vinylindoles to Annellated Indole Derivatives'; Part V: [I].

Section: Parentsmentioning

confidence: 89%

First Synthesis of 2‐Vinylindole and its diels‐Alder Reactions with CC‐Dienophiles

Eitel

1988

Self Cite

“…The reaction of 2e with 3 yields a mixture of the new indolyl-substituted 1,4-dihydro-1,2-pyridazines 10a and 10b which can be separated. This reaction probably also proceeds through [4 + 21 cycloaddition and [4 + 21 cycloreversion to form the intermediate VIII which subsequently undergoes stabilization by way of [ 1,3]-prototropic shifts to furnish the two tautomers 10a and lob. The products 10a and 10b were separated by flash chromatography and are thermodynamically very stable; they do not undergo equilibration in solution within the limits of the 400-MHz 'H-NMR detection.…”

Section: Mementioning

confidence: 98%

Locoselective [4 + 2] Cycloadditions of Vinylindoles with Inverse Electron Demand: A new access of indolyl‐substituted and annellated pyridazines

Pfeuffer

Kim

1989

Self Cite

Dedicated to Prof. Dr. C. H . Erieskorn (Wiirzburg, FRG) on the occasion of his 75th birthday (lO.X.88) 2-Vinylindole (la) and its donor-and acceptor-substituted (E)-derivatives 1b-e react highly locoselectively with dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate (3) to form the novel (indol-2-y1)-1,4-dihydropyridazines 4a and 7 as well as the heterocyclic annellated pyridazines 4b, 5, and 6. The reactions of the structurally related 3-vinylindoles 2a-e with 3 also gave rise to new indol-3-ylpyridazines 8, 9, and 10. The locoselectivities of these Dzels-Alder reactions were controlled mainly by steric effects.Introduction. -2-and 3-Vinylindoles I and I1 are heterocyclic dienes and, thus,

“…General. Methods for the preparation of 3-vinylindoles are described in [6] -lO-(phenylsulfonyl)-l.2.3.3a~,4,10,lOa~,lOb~-octahydropyrrolo[3,4-a]carbazole-1,3-dione (2). N -Phenylmaleimide (NPMI; 0.66 g, 3.8 mmol) in xylene (15 ml) was heated under reflux with l-(phenylsulfonyl)-3vinylindole (1; 0.9 g, 3.1 mmol) for 6.5 h. The precipitate was then separated and recrystallized from benzene: 0.…”

Section: Experimental Partmentioning

confidence: 99%

“…Scheme 1 PhO, 5 NPMI -Xylene. llOa 1 2 60% ') 2,Part V in the series 'Cycloadditions of Vinylindoles to Annellated Indole Derivatives'; Part IV: [2]. The N-unprotected parent compound, 3-vinylindole, exhibits a pronounced tendency to undergo dimerization and oligomerization 141, although MNDO calculations performed by us predict a good thermodynamic stability ( A H f = 72.9 kcal/mol) [5].…”

mentioning

confidence: 99%

New Reactions of 3‐Vinyl‐ and 3‐(2‐Propenyl)Indoles with N‐Phenylmaleimide: [4 + 2] Cycloaddition, ene reaction, and dimerization

Pfeuffer

1988

Self Cite

(1 1. I. 88) Depending on the substitution pattern of the aminobutadiene subunit in the selected 3-vinylindoles 1,3,6, and 9, stereospecific [4 + 21 cycloadditions ('endo'-preference) and dimerizations take place on reaction with Nphenylmaleimide. In the reaction of 9 with N-phenylmaleimide in the absence of a Lewis-acid catalyst, a competing ene reaction occurs in addition to the Diefs-Alder reaction.The Diels-Alder reaction of vinylindoles has now been established by others [ 11 and by us [l] [2] as a synthetically attractive concept for the preparation of [blannellated indole derivatives. However, the limits to the synthetic potential of this reaction type have by no means been defined. Also, comprehensive knowledge of alternative pathways for or of reactions competing directly with the cycloadditions when using vinyl-heterocycles and dienophiles is still lacking. For this reason and in continuation of our investigations on this subject [2], we now report on new results of the reactions of 1-phenylsulfonyl-3-vinylindole (1) and the 3-( 1-methylviny1)indoles 3,6, and 9 with N-phenylmaleimide (NPMI).The stabilized, N-protected, parent 3-vinylindole 12), in contradiction to a recently The N-unprotected parent compound, 3-vinylindole, exhibits a pronounced tendency to undergo dimerization and oligomerization 141, although MNDO calculations performed by us predict a good thermodynamic stability ( A H f = 72.9 kcal/mol) [5]. All 'endo'-cycloadducts 2,7, and 10 described here were formed in > 99.5% diastereoisomeric excess (d.e.; as determined by quantitative TLC remission measurements on silica-gel plates).')