Alder-ene reaction, intramolecular

Transition Metal-Catalyzed Intramolecular Alder-Ene Reactions 568... 

The Alder-ene reaction has traditionally been performed under thermal conditions—generally at temperatures in excess of 200 °C. Transition metal catalysis not only maintains the attractive atom-economical feature of the Alder-ene reaction, but also allows for regiocontrol and, in many cases, stereoselectivity. A multitude of transition metal complexes has shown the ability to catalyze the intramolecular Alder-ene reaction. Each possesses a unique reactivity that is reflected in the diversity of carbocyclic and heterocyclic products accessible via the transition metal-catalyzed intramolecular Alder-ene reaction. Presumably for these reasons, investigation of the thermal Alder-ene reaction seems to have stopped almost completely. For example, more than 40 papers pertaining to the transition metal-catalyzed intramolecular Alder-ene reaction have been published over the last decade. In the process of writing this review, we encountered only three recent examples of the thermal intramolecular Alder-ene reaction, two of which were applications to the synthesis of biologically relevant compounds (see Section 10.12.6). 

In the same manner, the natural products (—)-protometinol analogue [16] (Scheme 9.6) and (—)-gibboside [17] were synthesized utilizing an intramolecular Alder-ene reaction in the key step. However, the synthesis of the cyclization... 

Decatrienes, in intramolecular Alder-ene reactions, 10, 578 Dechlorination reactions, via cobalt(III) complexes, 7, 44 Decomposition pathways mixed metal carbonyls, via sonochemistry, 1, 310 in mononuclear ruthenium and osmium alkenyl formations, 6, 405... 

Inter-ring metal migrations, dynamic NMR studies, 1, 412 Intracyclic germanium-carbon bond formation large rings, 3, 706 small rings, 3, 703 Intramolecular Alder-ene reactions with metals, 10, 576 with palladium, 10, 568 with rhodium, 10, 575 with ruthenium, 10, 572 with transition metal catalysts, 10, 568 Intramolecular allylations, in cyclizations, with indium compounds, 9, 679... 

Pd-catalyzed Intramolecular Alder-ene Reaction of 1,6- and 1,7-Diynes and Enynes... 

The intramolecular Alder-ene reaction (enyne cydoisomerization reaction) with alkynes as the enophiles has found wide application compared with diene systems. The reason may be the ready chemo-differentiation between alkene and alkyne functionality and the more reactive alkyne moiety. Furthermore, the diene nature of the products will promote further applications such as Diels-Alder reactions in organic synthesis. Over the past two decades the transition metal-catalyzed Alder-ene cycloisomerization of l,n-enynes (typically n= 6, 7) has emerged as a very powerful method for constructing complicated carbo- or heterocydic frameworks. The transition metals for this transformation indude Pd, Pt, Co, Ru, Ni-Cr, and Rh. Lewis acid-promoted cydoisomerization of activated enynes has also been reported [11],... 

Highly enantioselective Rh-catalyzed intramolecular Alder-ene reactions for the synthesis of chiral 3-alkylidene-4-vinyltetrahydrofurans were reported by Zhang, as illustrated below <02AG(E)3457>. Metallic indium was also shown to mediate the intramolecular cyclization of tethered allyl bromides onto terminal alkynes to afford 3-methylene-4-vinyltetrahydrofurans in 50-62% yield <02SL2068>. 

Intramolecular Alder Ene Reactions with a Nitrogen Tether... 

Rhodiumcq-catalysed INTRAMOLECULAR ALDER-ENE reaction and syntheses of functionalised a-METHYLENE-y-BUTYROLACTONES AND CYCLOPENTANONES... 

A highly enantioselective and general rhodium(I)-catalysed intramolecular Alder-ene reaction has been developed. a-Methylene-y-butyrolactones, a-methyl-ene-y-butyrolactams, polyfunctional cyclopentanes, cyclopentanones, and functionalized tetrahydrofurans were formed in high yields and excellent enantiomeric... 

An alkene isomerization/enantioselective intramolecular Alder-ene reaction cascade occurs using a cationic rhodium(I)/(7 )-BINAP complex as catalyst (Scheme 150). 0... 

There has been a report of the use of ionic liquids to expedite the metal catalyzed intramolecular Alder-Ene reaction. In this work, an Ir catalyst was used, the yields for the conversion of 146 into 147 were high and the use of the ionic liquid served to reduce the temperature required by... 

In comparison to the intramolecular Diels-Alder reaction, the intramolecular Alder ene reaction has been little studied (1,2). All examples in the hterature through mid-1981 are included in the Tables at the end of this chapter. 

Diastereomeric control in the intramolecular Alder ene reaction, influence of a chiral acceptor 70... 

---