Pyridines via Fischer Carbene complexes.- W(CO)<sub>6</sub>-Mediated Cycloadditions of Enamines to Alkynes<i>via</i>Alkynylcarbene and 1,2-Dihydropyridin-2-ylidene Complexes

Aumann, Rudolf; Roths, Klaus; Grehl, Matthias

doi:10.1055/s-1993-22566

Cited by 39 publications

(9 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The short trans -CO (M1 Ã/C5) bond in 1b and 11a also illustrates the strong donor ability of the terminal substituents. Like in 1,2-dihydropyridinylidene complexes [22] the dihydropyridinyl ring in 11a is essentially planar.…”

Section: Propertiesmentioning

confidence: 94%

A new method for the preparation of N-stabilized allenylidene complexes of chromium and tungsten

Fischer¹,

Szesni²,

Roth³

et al. 2003

Journal of Organometallic Chemistry

View full text Add to dashboard Cite

Displacement of tetrahydrofuran in [(CO) 5 M(THF)] (M 0/Cr, W) by the anion [C Å/C Ã/C(Ä/X)Y] ((X 0/O; NR; Y 0/NR ? 2 , Ph) followed by alkylation of the resulting metalate with [R ƒ 3 O]BF 4 (R ƒ0/Me, Et) offers a convenient and versatile route to p-donorsubstituted allenylidene complexes, [(CO) 5 M Ä/C Ä/C Ä/C(XR ƒ)Y]. Allenylidene complexes in which the terminal carbon atom of the allenylidene ligand constitutes part of a heterocycle are likewise accessible by this reaction sequence. Reaction of [(CO) 5 M(THF)] with Li[C Å/C Ã/C(Ä/NMe)Ph] (and subsequent protonation of the metalate afford [(CO) 5 M Ä/C Ä/C Ä/C(NMeH)Ph] in high yield. As indicated by the spectroscopic data of the compounds and the X-ray analyses of three representative examples, these allenylidene complexes are best described as hybrids of allenylidene and zwitterionic alkynyl complexes with delocalisation of the electron pair at nitrogen towards the metal center. Dimethylamine reacts with the amino(phenyl)allenylidene complex [(CO) 5 Cr Ä/C Ä/C Ä/ C(NMe 2)Ph] (7a) by addition of the amine across the C a Ä/C b bond to give selectively the E-alkenyl(amino)carbene complex [(CO) 5 Cr Ä/C(NMe 2) Ã/CH Ä/C(NMe 2)Ph] (12). In contrast, the reaction of dimethylamine with the amino(methoxy)allenylidene complex [(CO) 5 Cr Ä/C Ä/C Ä/C(NMe 2)OMe] (1a) proceeds by addition of the amine to the C g atom and subsequent elimination of methanol to give the substitution product [(CO) 5 Cr Ä/C Ä/C Ä/C(NMe 2) 2 ] (13). Triphenylphosphane neither adds to the C a nor the C g atom of 7a but upon irradiation displaces a CO ligand to form a cis-allenylidene(tetracarbonyl)phosphane complex 15.

show abstract

Section: Propertiesmentioning

confidence: 94%

A new method for the preparation of N-stabilized allenylidene complexes of chromium and tungsten

Fischer¹,

Szesni²,

Roth³

et al. 2003

Journal of Organometallic Chemistry

View full text Add to dashboard Cite

show abstract

“…Recently, a highly regioselective 3 + 2 cyclopentadiene annulation method was reported, which is based on the addition of (1-alkynyl)carbene complexes (=C3 unit) to cycloalkenyl amines **CC(NR 2 )*** (=C2 unit) . The key step of this reaction involves formation of 1-metalla-1,3,5-hexatrienes (CO) 5 MC(OEt)CHC(Ph)(**)CC(NR 2 )*** by Michael-type addition of the enamine to the C⋮C bond of the (1-alkynyl)carbene complex, which subsequently undergoes cyclization to cyclopentadiene complexes. Formation of cyclopentadienes in a 3 + 2 fashion is achieved also by reaction of alkynes R 1 C⋮CH (=C2 unit) with 4-amino 1-chroma 1,3-dienes [=(enamino)carbene complexes] (CO) 5 CrC(OEt)CHC(NR 2 )R (=C3 unit), but the regiochemistry of the “alkyne route” is different from that of the “enamine route”, since 1-metalla-1,3,5-hexatriene key intermediates (CO) 5 MCR 1 CHC(OEt)CHC(NR 2 )R are generated with different regiochemistry by insertion of the alkyne R 1 C⋮CH into the MC bond of the 1-metalla-1,3-diene …”

mentioning

confidence: 99%

Organic Syntheses via Transition Metal Complexes. 89.¹ 5-Aza-1-metalla-1,3,5,7-octatetraenes and 2H-Pyrrole and 2H-Dihydroazete Complexes from (1-Alkynyl)carbene Complexes (M = Cr, W) and Alkenyl N-H Imidates

1997

Self Cite

View full text Add to dashboard Cite

Addition of alkenyl N-H imidates RCHCR1C(OEt)NH (8a − d; R, R1 = Ph, Me, H) to (1-alkynyl)carbene complexes (CO)5MC(OEt)C⋮CPh (6a,b; M = Cr, W) affords novel 5-aza-1-metalla-1,3,5,7-octatetraenes (CO)5MC(OEt)CHC(Ph)NC(OEt)CR1CHR ((Z)-9a − h; by Michael addition) together with 2,5-diethoxy-2H-pyrrole complexes 10a − h (by 3 + 2 cycloaddition) as well as 2,4-diethoxy-2H-dihydroazete complexes 11e − h (by 2 + 2 cycloaddition) in good overall yields. The product ratio 9:10:11 is strongly influenced by the nature of the metal (chromium or tungsten). Thus, formation of 5-aza-1-metalla-1,3,5,7-octatetraenes 9 is favored in the case of M = W, while 2H-dihydroazete complexes 11 are major products in the case of M = Cr. Compounds 9a − d undergo smooth cyclization at 80−90 °C to give 2,3-diethoxy-2H-pyrrole complexes 12a − d (which are regioisomers of 10a − d) in 86−93% yields, from which (metal-free) 2H-pyrroles 13a − d are generated on thermolysis at 110 °C. X-ray structure analyses are reported for the 5-aza-1-metalla-1,3,5,7-octatetraene 9b, the (regioisomeric) 2H-pyrrole complexes 10b and 12b, and the 2H-dihydroazete complex 11e.

show abstract

“…According to Inglesby, [103,104] [3+3] cycloadditions are considered of higher order as long as the use of three‐atom synthons as anion/cation fragments allows for the cycloadditions. As a consequence, very few reports are found on [3+3] cycloaddition with carbenes [105,106] . The corresponding ring is medium‐sized, in agreement with the Wender definition [23] .…”

Section: Fischer Carbene Complexes With Metal‐mediated Higher‐order Cycloadditionsmentioning

confidence: 55%

Fischer Carbene Complexes: A Glance at Two Decades of Research on Higher‐Order Cycloaddition Reactions

Feliciano

Vázquez

Benítez‐Puebla

et al. 2021

Chemistry A European J

View full text Add to dashboard Cite

The structure of Fischer carbene complexes (FCCs) is electron deficient. If bearing an α,β‐unsaturated system, it can generate a wide variety of compounds by undergoing many different transformations, including higher‐order cycloadditions. The latter are described as pericyclic reactions in which more than six electrons participate. These reactions have been employed in various areas of organic synthesis, resulting in highly selective compounds with a broad range of scaffolds. The first studies on higher‐order cycloadditions involving FCCs frequently yielded competing byproducts. Many groups have attempted to increase selectivity by exploring distinct reaction conditions, reagents and co‐catalysts (e. g., metal‐mediated cycloadditions). The present review is the first to focus exclusively on using higher‐order cycloadditions involving FCCs to synthesize carbocycles and heterocycles. Based on two decades of reports, an analysis is made of the main aspects of the mechanisms proposed for higher‐order cycloadditions and the structural diversity obtained by the substituent effect.

show abstract

Pyridines via Fischer Carbene complexes.- W(CO)₆-Mediated Cycloadditions of Enamines to AlkynesviaAlkynylcarbene and 1,2-Dihydropyridin-2-ylidene Complexes

Cited by 39 publications

References 0 publications

A new method for the preparation of N-stabilized allenylidene complexes of chromium and tungsten

A new method for the preparation of N-stabilized allenylidene complexes of chromium and tungsten

Organic Syntheses via Transition Metal Complexes. 89.¹ 5-Aza-1-metalla-1,3,5,7-octatetraenes and 2H-Pyrrole and 2H-Dihydroazete Complexes from (1-Alkynyl)carbene Complexes (M = Cr, W) and Alkenyl N-H Imidates

Fischer Carbene Complexes: A Glance at Two Decades of Research on Higher‐Order Cycloaddition Reactions

Contact Info

Product

Resources

About

Pyridines via Fischer Carbene complexes.- W(CO)6-Mediated Cycloadditions of Enamines to AlkynesviaAlkynylcarbene and 1,2-Dihydropyridin-2-ylidene Complexes

Cited by 39 publications

References 0 publications

A new method for the preparation of N-stabilized allenylidene complexes of chromium and tungsten

A new method for the preparation of N-stabilized allenylidene complexes of chromium and tungsten

Organic Syntheses via Transition Metal Complexes. 89.1 5-Aza-1-metalla-1,3,5,7-octatetraenes and 2H-Pyrrole and 2H-Dihydroazete Complexes from (1-Alkynyl)carbene Complexes (M = Cr, W) and Alkenyl N-H Imidates

Fischer Carbene Complexes: A Glance at Two Decades of Research on Higher‐Order Cycloaddition Reactions

Contact Info

Product

Resources

About

Pyridines via Fischer Carbene complexes.- W(CO)₆-Mediated Cycloadditions of Enamines to AlkynesviaAlkynylcarbene and 1,2-Dihydropyridin-2-ylidene Complexes

Organic Syntheses via Transition Metal Complexes. 89.¹ 5-Aza-1-metalla-1,3,5,7-octatetraenes and 2H-Pyrrole and 2H-Dihydroazete Complexes from (1-Alkynyl)carbene Complexes (M = Cr, W) and Alkenyl N-H Imidates