Mesoionic Pyrrolium Complexes and Dihydropyrroles by Cycloaddition of (Non-enolizable) Imines to an [(1-Alkynyl)carbene]tungsten Complex

Aumann, Rudolf; Yu, Zhengkun; Fröhlich, Roland; Zippel, Frank

doi:10.1002/(sici)1099-0682(199811)1998:11<1623::aid-ejic1623>3.0.co;2-p

Cited by 17 publications

(18 citation statements)

References 16 publications

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“…Two further modes, paths b and c, for the opening of the hetero-1-metalla-1,3,6-heptatrienes, which may be of inter-1,3-diene) was shown to form a stable homooxazoline ( ϭ 2-oxa-4-aza-bicyclo[3.1.0]hexene) on thermolysis. [48] Scheme 39. 2,4-Heptadien-1,7-diones by fragmentation of 5-oxa-1chroma-1,3,6-heptatrienes est for synthetic applications, are shown in Schemes 39Ϫ43.…”

Section: Cyclization Reactions Involving a Side Chainmentioning

confidence: 99%

1-Metalla-1,3,5-hexatrienes and Related Compounds

Aumann¹

2000

Eur. J. Org. Chem.

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Section: Cyclization Reactions Involving a Side Chainmentioning

confidence: 99%

1-Metalla-1,3,5-hexatrienes and Related Compounds

Aumann¹

2000

Eur. J. Org. Chem.

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“…3d. 1 (1:1:2:1:1: 1:1:1, CH each, C 6 H 5 and C7 to C10), 100.4 (CH, C2), 82.8 (C q , C10b), 64.5 (OCH 2 ), 54.1 and 53.5 (NCH 2 each, broad); 35.5, 29.9 and 28.6 (CH 2 each, C4 to C6), 24.6 and 22.8 (2 NCH 2 CH 2 , broad), 14.9 (OCH 2 CH 3 ), 12.1 (2 NCH 2 CH 2 CH 3 ).…”

Section: Scheme 2 (5) Typical Procedures: Pentacarbonyl[ethoxy(5-diprmentioning

confidence: 99%

Organic Syntheses via Transition Metal Complexes, 98. Unprecedented Rearrangement of (1,3-Butadien-2-yl)carbene into (1,3-Butadien-1-yl)carbene Complexes (M = Cr; W)

Aumann¹,

Kößmeier²,

Jäntti³

1998

Synlett

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2-Aminocyclonona-1,8-dienyl carbene complexes 3a-d are generated by addition of cycloheptenylamines 2a-d to (1-alkynyl)carbene complexes (CO) 5 M=C(OEt)C≡CPh 1a,b (M = W, Cr) in pentane. Compounds 3 are stable in solid state but in solution undergo ring contraction of the nine-membered ring to give (2-aminocycloheptenyl)alkenyl carbene complexes 4a-d which subsequently are transformed into tetrahydroazulenes 5 by elimination of the metal unit. The reaction of 3-aminocyclohexenones 6 with the tungsten compound 1a leads to generation of cyclooctadienon-1-yl carbene complexes 7, from which 5-amino-7,8-dihydrochromylidene complexes 8 are obtained (instead of cyclopentadienes). These transformations rest on a hitherto unknown rearrangement of a (1,3-butadien-2-yl)carbene-into a (1,3-butadien-1-yl)carbene complex.(1-Alkynyl)carbene complexes (CO) 5 M=C(OEt)C≡CPh 1a,b (M = W, Cr) have been applied as stochiometric reagents in a number of highyield transformations which are potentially useful in organic synthesis. 2 For example, it has been shown recently that cyclopentadienes can be generated in [3+2] fashion by reaction of compounds 1 with cyclic tertiary enamines in solvents like dichloromethane. 3c,g (Conjugated) 1-metalla-1,3,5-hexatrienes (CO) 5 M=CC=CC=C [= (1,3-butadien-1-yl)carbene complexes] were found to be key-intermediates in these transformations. 3 In subsequent studies on reactions of compounds 1 with open-chain tertiary enamines and enaminones, respectively, crossconjugated metallatrienes (CO) 5 M=CC(=C)C=C [= (1,3-butadien-2-yl)carbene complexes] were generated instead of conjugated metallatrienes, if the reactions were carried out in pentane. 4 We now wish to report on reactions of compounds 1 with cyclic enamines, in which conjugated as well as cross-conjugated metallatrienes are obtained depending on the reaction conditions. We found that crossconjugated metallatrienes 3 and 7, respectively, are isolated in high yields from reactions of compounds 1 with cyclic enamines 2 and cyclic enaminones 6, respectively, if these reactions are carried out in solvents, like pentane, in which these compounds are sparsely soluble and are therefore precipitated from the reaction mixture. Interestingly, if compounds 3 and 7 are kept in solution they are transformed into conjugated metallatrienes, from which cyclopentadienes 5 and chromenylidene complexes 8, respectively, are finally obtained. Based on the unanticipated fact that a cross-conjugated metallatriene can be converted into a conjugate metallatriene, now light is shed on quite a number of potential applications of cross-conjugated metallatrienes in transformations related to the formation of cyclopentadienes 5 from compounds 3 (Scheme 1).Reaction of a (1-alkynyl)carbene complex 1a,b with a 1-aminocycloheptene 2a-d in pentane leads to precipitation of yellow cyclonona-1,8-dien-1-yl carbene complexes 3 in good yields (Scheme 1). 5 Compounds 3 are stable in solid state, but in solution they readily form compounds 4 by a hitherto unknown rearrangement of a cro...

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“…Although, the [2+2] cycloaddition of alkynes and imines appears to be a convenient route to this type of heterocyclic framework, only a few specific examples have been reported; in these cases, electron‐rich alkynes, as ynamines,6 alkynyl selenides,7 or alkynyl sulphides,8 are able to form the expected 2‐azetine skeleton, which is not isolated but rapidly opens to the azadiene system. The [2+2] cycloaddition of electron‐poor alkynes and imines has only previously been suggested as an intermediate in the cyclization reaction between an alkynyl(ethoxy)carbene of tungsten and imine fluorenones to afford pyrroline derivatives 9…”

Section: Methodsmentioning

confidence: 99%

Sequential Five‐Component Construction of the Cyclopenta[e][1,3]oxazine Skeleton using Stable 2‐Azetine Derivatives

et al. 2010

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Dedicated to Professor Julius Rebek, Jr. on the occasion of his 65th birthday Small-ring heterocycles are of prominent importance because of their potential as bioactive compounds and synthetic building blocks. Whilst the chemistry of three-membered nitrogen heterocycles has been widely reported, studies on their four-membered counterparts have focused primarily on 2-azetidinones and, to a much lesser extent, azetidine rings. [1] The 2-azetine system 1,2-dihydroazete, which has a strained cyclic enamine ring, is particularly elusive. [2] Most 2-azetine compounds undergo spontaneous electrocyclic ring opening to afford their 1-azadiene analogues; as such, there are few examples of stable 2-azetines in the literature and those reported require electron-withdrawing substituents, for example, carbonyl, carboxyl, sulfonyl, or nitro groups, attached to the nitrogen atom. [3,4] As a consequence, the chemistry of 2azetines remains largely unexplored, and has been predominantly focused on their potential as a precursor to azadienes. Moreover, there are no general synthetic routes to 2azetines. [5] Although, the [2+2] cycloaddition of alkynes and imines appears to be a convenient route to this type of heterocyclic framework, only a few specific examples have been reported; in these cases, electron-rich alkynes, as ynamines, [6] alkynyl selenides, [7] or alkynyl sulphides, [8] are able to form the expected 2-azetine skeleton, which is not isolated but rapidly opens to the azadiene system. The [2+2] cycloaddition of electron-poor alkynes and imines has only previously been suggested as an intermediate in the cyclization reaction between an alkynyl(ethoxy)carbene of tungsten and imine fluorenones to afford pyrroline derivatives. [9] As part of our interest in Fischer-type metal carbenes, we have recently considered more-electrophilic metal carbenes, the so-called non-heteroatom-stabilized carbenes. [10] These compounds are particularly useful in organic synthesis, and our preliminary results have revealed significant differences in the reactivity of both heteroatom- [11] and non-heteroatomstabilized systems.Herein, we report the [2+2] cycloaddition reaction of alkynyl-substituted (pentacarbonyl)chromium or -tungsten carbene complexes with imines as a suitable procedure for accessing stable 2-azetine derivatives. Moreover, the conjugation of the resulting azetine unit with the metal carbene allows for a facile synthesis of novel cyclopenta[e]-[1,3]oxazines involving treatment with alkynes. This threecomponent process (azetine, alkyne, and CO ligand) features cleavage of the azetine C3 À C4 bond, rather than the expected N À C4 bond, and the formation of three C À C bonds and one CÀO bond (Scheme 1).Stable, easy-to-handle methoxycarbenes 1 are used as in situ precursors of alkynylcarbenes 3 using the methoxyacetylide 2 exchange reaction ( Table 1). The resultant solution of 3 in tetrahydrofuran was treated at À80 8C with 1.3-5.0 equivalents of imine 4 (see the Supporting Information) and the mixture was allowed to warm to 0 8C....

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Mesoionic Pyrrolium Complexes and Dihydropyrroles by Cycloaddition of (Non-enolizable) Imines to an [(1-Alkynyl)carbene]tungsten Complex

Cited by 17 publications

References 16 publications

1-Metalla-1,3,5-hexatrienes and Related Compounds

1-Metalla-1,3,5-hexatrienes and Related Compounds

Organic Syntheses via Transition Metal Complexes, 98. Unprecedented Rearrangement of (1,3-Butadien-2-yl)carbene into (1,3-Butadien-1-yl)carbene Complexes (M = Cr; W)

Sequential Five‐Component Construction of the Cyclopenta[e][1,3]oxazine Skeleton using Stable 2‐Azetine Derivatives

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