Transition metal-catalyzed formation

Indeed, a Stille reaction of the TES-protected ( )-bromoxone (6/1-175) with the stannane 6/1-173 led to 6/1-176 upon standing overnight, via the diene 6/1-172 (Scheme 6/1.46). This synthesis is a classic example of a transition metal-catalyzed formation of a 1,3-diene, followed by a cycloaddition. 

The chemistry of cyclopropanol [7] has long been studied in the context of electrophilic reactions, and these investigations have resulted in the preparation of some 3-mercurio ketones. As such mercury compounds are quite unreactive, they have failed to attract great interest in homoenolate chemistry. Only recent studies to exploit siloxycyclopropanes as precursors to homoenolates have led to the use of 3-mercurio ketones for the transition metal-catalyzed formation of new carbon-carbon bonds [8] (vide infra). 

A significant part of the examples of transition metal catalyzed formation of five membered heterocycles utilizes a carbon-heteroatom bond forming reaction as the concluding step. The palladium or copper promoted addition of amines or alcohols onto unsaturated bonds (acetylene, olefin, allene or allyl moieties) is a prime example. This chapter summarises all those catalytic transformations, where the five membered ring is formed in the intramolecular connection of a carbon atom and a heteroatom, except for annulation reactions, involving the formation of a carbon-heteroatom bond, which are discussed in Chapter 3.4. 

Examples of the transition metal catalyzed formation of carbon-heteroatom bonds other than carbon-nitrogen are less abundant. In a recent survey of the copper catalyzed carbon-oxygen bond formation between alcohols and organotrifluroborates the coupling of 3-thienyltrifluoroborate and 2-furfuryl alcohol gave the expected thienyl-furfuryl-ether in good yield (6.83.),113... 

Heating borazine in vacuo at 70°C yields poly(borazylene) polymers, which are soluble in solvents such as tetrahydrofuran or glyme and could be thermolyzed to boron nitride in good yields (120). Other soluble preceramic polymers were produced by transition-metal catalyzed formation of B-alkenylborazines (eq. 34) which were thermally polymerized under mild conditions to poly(alkenylborazines). The latter yielded boron nitride having low carbon contents when thermolyzed in an ammonia atmosphere (121). 

The transition-metal-catalyzed formation of 1,3-dioxepanes from vinyl ethers has also been described . For example, reaction of allyl ether 426 with a nonhydridic ruthenium complex at higher temperatures and without any solvent produce 1,3-dioxepane 427 (Scheme 197). It was suggested that cyclic acetal formation proceeds via a -allyl-hydrido transient complex, which undergoes nucleophilic attack by the OH group at the coordinated -allyl <2004SL1203>. 

A facile transition metal-catalyzed formation of C-N bonds has been reported <2005T2931>. 3-Bromothiophene can be coupled with 2-pyridone to form the A -(3-thienyl) derivative in a Cul-catalyzed reaction. The catalyst consists of Cul in the presence of T,Ar -dimethylcyclohexane-l,2-diamine and KOAc or K2CO3 (Equation 39). 

TRANSITION METAL CATALYZED FORMATION OF FORMIC ACID AND ITS DERIVATIVES FROM CO AND Hj... 

Transition Metal Catalyzed Formation of Formic Acid and its Derivatives from CO2 and H2... 

In 1970 the transition metal catalyzed formation of alkyl formates from CO2, H2, and alcohols was first described. Phosphine complexes of Group 8 to Group 10 transition metals and carbonyl metallates of Groups 6 and 8 show catalytic activity (TON 6-60) and in most cases a positive effect by addition of amines or other basic additives [26 a, 54-58]. A more effective catalytic system has been found when carrying out the reaction in the supercritical phase (TON 3500) [54 a]. Similarly to the synthesis of formic acid, the synthesis of methyl formate in SCCO2 is successful in the presence of methanol and ruthenium(II) catalyst systems [54 b]. 

This section focuses on the transition metal-catalyzed formation of ring systems using alkynes in the homogeneous phase. Because of the great number of possible products, this survey is restricted to five- and six-membered heterocycles, and six-and eight-membered carbocycles. 

Pang, W., Zhu, S., Jiang, H. and Zhu, S. (2006) Transition metal-catalyzed formation of CF3-substituted P-unsaturated alkene and the synthesis of a-trifluoromethyl-substituted P-amino ester. Tetrahedron, 62, 11760-11765. 

Jaska CA, Temple K, Lough AJ, Manners I (2003) Transition metal-catalyzed formation of boron-nitrogen bonds catalytic dehydrocoupling of amine-borane adducts to form aminoboranes and borazines. J Am Chem Soc 125 9424—9434... 

The transition-metal-catalyzed formation of pyridine-type six-membered rings was reported by Mukhopadhyay and Kundu in 2000 [94], Bis-tosylamides of 1,2-diaminobenzene derivatives 193 undergo an unusual pyrazine formation by 6-exo-dig cyclization to give l-(quinoxalin-2-yl)ketones 194 in moderate yields by treatment with 10 mol % Cul in the presence of K2CO3 (Scheme 19.49). A reaction mechanism was not proposed. 

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