Organic Syntheses via Transition Metal Complexes. 83.¹ cis-1-Metalla-1,3,5-hexatrienes (Butadienylcarbene Complexes) of Tungsten via Ring Opening of Pyranylidene Complexes

Abstract

Aminolysis of the 2H-pyran-2-ylidenetungsten complex 3 affords amino-1-tungsta-1,3,5-hexatrienes with different structures, depending on the reaction temperature and the type of amine involved. Addition of primary amines RNH2 (4a − d) (R = allyl, n-Bu, CH2Ph, i-Pr) to 3 at −15 °C yields salt-type (3Z)-6-amino-1-tungsta-1,3,5-hexatrienes 5a − d by reversible ring opening of the pyranylidene ring. Addition of 4a − c at 20 °C affords (3Z)-2-amino-1-tungsta-1,3,5-hexatrienes 6a − c by an irreversible ring opening of the pyranylidene ring. Secondary amines RR1NH 8a − c [RR1N = Me2N, 2-(hydroxymethyl)pyrrolidine, pyrrolidine] undergo an irreversible ring opening to 2-amino-1-tungsta-1,3,5-hexatrienes 9a − c. Aminolysis of 3 in the presence of Me3SiCl/Et3N affords acetimino pyranylidene complexes 10, from which (3Z)-2,6-diamino-1-tungsta-1,3,5-hexatrienes 11 are derived upon aminolysis. Thermolysis of 6a in THF/pyridine affords the captodative 1-amino-1,3-hexadien-5-one 12. 2H-Pyran-2-ylidene complex 3, C19H12O7W, was characterized by X-ray diffraction.

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

“…2.193(5). [13] In line with the mesoionic character of compound 3b is the pattern of Scheme 2. Two different routes to pyrrole derivatives from non-alternating bond lengths found in the N-heterocyclic ring …”

“…The mesoionic character of the novel pyrrolium compounds 3 is indicated in its 13 C-NMR spectrum by a characteristic upfield shift of the signal WϪC(ring) (3a: δ ϭ…”

Organic Syntheses via Transition Metal Complexes. 95.1 Rearrangement of (Cyclobutenyl)carbene Tungsten Complexes to 1-Tungsta-1,3,5-hexatrienes

“…(1-Alkynyl)carbene complexes (CO) 5 MC(OEt)C⋮CPh ( 1a , b ) (M = W, Cr) have been applied as building blocks in a manifold of reactions, which are potentially useful for organic synthesis . It was found only recently that, for example, amino cyclopentadienes, 2a,,,,7c ,,,7c 2,3-homopyrroles,7b and pyran-2-ylidene complexes 5-7 are generated in high yields by addition of (1-alkynyl)carbene complexes 1 to tertiary enamines −CHC(NR 2 )− and secondary enaminones, respectively , path b), resulting from addition of the enamine to the C⋮C bond of compound 1 , were shown to be key intermediates in these reactions.…”

1-Lithio-1,3-dienes as useful building blocks in organic synthesis

“…Among the family of Fischer-type carbene complexes, six-membered pyranylidene carbene complexes of the group 6 metals Cr, Mo, and W have recently attracted increasing interest due to their utilization in ring-opening reactions [13], Diels-Alder reactions [14], and 1,6-addition [15]. On the other hand, demetalation of Fischer carbene complexes is of significant interest because cleavage of the multiple bond between the metal and the carbene carbon atom provides an important method to prepare useful organic molecules [12].…”