Enaminone Substituents Attached to Cyclopentadienes:3E/3Z Stereochemistry of 1-Metalla-1,3,5-hexatriene Intermediates (M=Cr, W) as a Functional Criterion for the Formation of Cyclopentadienes and Six-Membered Heterocycles, Respectively

Abstract

Reactions of NH-enaminones 2 with [2-(1-cycloalkenyl)ethynyl]carbene complexes 7 (M=W, Cr) gave tetrahydropentalenes, tetrahydroindenes, and hexahydroazulenes 8a-i, in which the NH-enaminone moiety is attached to the cyclopentadiene unit. The reaction involved formation of (3E)-1-metalla-1,3,5-hexatriene intermediates, which underwent pi cyclization faster than 3E/3Z isomerization. Tungsten complexes 12 and 13 were characterized as reaction intermediates. Compounds 8 are potentially bidentate ligands with respect to coordination both of the cyclopentadienyl and the enaminone moieties.

β-Enamino Esters in Heterocyclic Synthesis: Synthesis of Pyrazolone and Pyridinone Derivatives

“…β -Enamino esters are versatile intermediates for the synthesis of nitrogen containing compounds [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. Also, they are important subunits present in some biologically important natural products as well as therapeutic agents [ 9 , 10 , 11 , 12 ].…”

Highly Selective Formation of [4+2] and [4+3] Cycloadducts of Tetrahydroindenes Generated in Situ from a (1-Alkynyl)carbene Tungsten Complex by the Metalla-1,3,5-hexatriene Route

“…This approach has been recently extended to include reactions of 1‐tungsta‐1,3‐butadienes, which were found to experience a strong reactivity enhancement under the influence of rhodium or copper catalysts 1, 7. Furthermore, a most versatile procedure for the anellation of cyclopentadiene rings was found; this involves formation of 1‐metalla‐1,3,5‐hexatrienes from [2‐(1‐cycloalkenyl)ethynyl]carbene complexes by addition of protic nucleophiles NuH,9, 15 for example, R′(RCO)CH 2 ,8 R 2 NH,9, 10 R 2 PH,9 RCOOH and ROH,11, 12 RCXSH (X=O, NH, NR),13 and RSH 14…”

Organic Syntheses via Transition-Metal Complexes. 110.1 A Convenient Regio- and Stereoselective Approach to the Angular Allylation of Bicyclic Cyclopentadienes Generated by the (1-Alkynyl)carbene Complex Route

“…Much effort has been made more recently to extend the scope of such reactions. A new and efficient approach to the formation of 1-metalla-1,3,5-hexatrienes from starting components other than enamines involves the addition of protic nucleophiles NuH [NuH = R(R‘CO)CH 2 , R 2 NH, R 2 PH, RC(O)OH and ROH, , RC(X)SH (X = O, NH, NR), and RSH] to [2-(1-cycloalkenyl)ethynyl]carbene complexes 1a − c . , This reaction mode provides a highly regioselective entry not only to a broad range of substituted cyclopentadienes not available up to date but also to very thermolabile bicyclic cyclopentadienes, which in our hands now prove to be valuable building blocks for the stereoselective generation of polycyclic ring compounds. The regio- and stereochemistry of the latter reactions is influenced not only by the substitution pattern of the cyclopentadiene ring but also by ring strain effects imposed by the annelated ring.…”