Carbon monoxide intermolecular reactions

Aryl- and alkenylcarbene complexes are known to react with alkynes through a [3C+2S+1C0] cycloaddition reaction to produce benzannulated compounds. This reaction, known as the Dotz reaction , is widely reviewed in Chap. Chromium-Templated Benzannulation Reactions , p. 123 of this book. However, simple alkyl-substituted carbene complexes react with excess of an alkyne (or with diynes) to produce a different benzannulated product which incorporates in its structure two molecules of the alkyne, a carbon monoxide ligand and the carbene carbon [128]. As referred to before, this [2S+2SH-1C+1C0] cycloaddition reaction can be carried out with diyne derivatives, showing these reactions give better yields than the corresponding intermolecular version (Scheme 80). 

The simplest primary alkyl cations, CHJ and C2H, are formed from methane and ethane, respectively, by SbPs—PHSO3 (Olah and Schlosberg, 1968 Olah et al., 1969) and by SbPs (Lukas and Kramer, 1971). In these cases, intermolecular electrophilic substitution of these ions at the precursor alkanes leads to oligocondensation products, e.g. tertiary butyl and hexyl ions. In the presence of carbon monoxide it has been found possible to intercept the intermediate CHJ and C2H quantitatively as oxocarbonium ions (Hogeveen et al., 1969 Hogeveen and Roobeek, 1972). The competition between the reactions of the ethyl cation with ethane and carbon monoxide, respectively, is illustrated by the following equations ... 

A few additional Pd-catalyzed schemes have been employed for Ilac type cyclization chemistry. Palladium-phenanthroline complexes were used by the Ragaini group to prepare indoles via the intermolecular cyclization of nitroarenes and alkynes in the presence of carbon monoxide <06JOC3748>. Jia and Zhu employed Pd-catalysis for the annulation of o-haloanilines with aldehydes <06JOC7826>. A one-pot Ugi/Heck reaction was employed in the preparation of polysubstituted indoles from a four-component reaction system of acrylic aldehydes, bromoanilines, acids, and isocyanides <06TL4683>. 

Khand and Pauson reported a Co-mediated intermolecular [2-I-2-I-1] cycloaddition of an alkyne, an alkene and carbon monoxide (the Pauson-Khand reaction) [4, 26] wherein an alkyne-Co2(CO)6 complex, which had been prepared from Co2(CO)g... 

The halogenated derivatives of six membered heterocycles, like their carbacyclic analogues, usually participate readily in coupling reactions that involve the incorporation of an olefin or carbon monoxide. The insertion of carbon monoxide commonly leads to the formation of either a carboxylic acid derivative or a ketone, depending on the nature of the other reactants present. Intermolecular and intramolecular variants of the insertion route are equally popular, and are frequently utilized in the functionalization of heterocycles or the formation of annelated ring systems. 

The domino carbonylation and Diels-Alder reaction described in Section 11.3.2.8 proceed only as an intramolecular version. Attempted carbonylation and intermolecular Diels-Alder reaction of the conjugated 4-en-2-ynyl carbonate 124 in the presence of various alkenes as dienophiles under 5 atm of carbon monoxide at room temperature gave entirely different products without undergoing the intermolecular Diels-Alder reaction. The 4-oxo-5-alkylidene-2-cyclopentenecarboxylate 125 was obtained unexpectedly by the incorporation of two molecules of carbon monoxide in 82% yield at 50 °C under 1 atm (Scheme 11-35) [32]. The use of bidentate ligands such as dppp or bis(diphenylphosphino)ethane (dppe) is important. Triphenylphosphine is ineffective for the reaction. 

Enantioselectivities up to 44 % were reached in intermolecular PKRs when chiral aminoxides R 3N—>0 were used [19]. Although the mechanism is not known, it seems likely that the chiral A-oxide discriminates between the prochiral carbonyl cobalt units, either oxidizing one carbon monoxide selectively to produce a vacant site for the alkene insertion, or stabilizing a vacant site on one of the cobalts preferentially. This approach was modified by application of chiral precursor substrates [20]. Albeit the synthesis of the latter is cumbersome, the concept was successfully applied in several total syntheses, for example of hirsutene [21], brefeldine A [22], /9-cuparenone [23], and (+)-15-norpentalenene [24] (eq. (10)). Stoichiometric amounts of the mediator compound Co2(CO)8 are still necessary in this useful version of the Pauson-Khand reaction. 

Various other rhodium catalysts can initiate hydroacylation reactions. Thus, the indenyl complex [075-C9H7)Rh(J72-C2H4)2] is used in intermolecular hydroacylation44. Rhodium zeolites (RhNaX and RhNaY type zeolites) act as bifunctional catalysts for the synthesis of 2-methyl-3-hexanone and 4-heptanone (1 2 ratio) from propene, carbon monoxide and hydrogen53. In this case, the ketones may be formed via hydrocarbonylation (vide supra), however, according to control experiments, rhodium-free zeolites alone catalyze ketone formation from propene and butyraldehyde53. 

A chiral auxiliary-based method employing heteroatom binding shows considerable promise in nonracemic intermolecular Pauson-Khand chemistry. Scheme 5-3 depicts an acetylene synthetic equivalent bearing the 10-methylthioisobomeol moiety (15), which is capable of significant asymmetric induction upon Pauson-Khand cycloaddition. Loss of carbon monoxide from 15 may be effected thermally, or better yet, by reaction with IV-methylmorpholine N-... 

In contrast to intramolecular carbonylative Mizoroki-Heck cyclizations, the intermolecular carbonylative reaction of aryl halides with alkenes has been much less explored. Figure 3.10 depicts one of these rare examples using a carbon monoxide pressure of 5 atm [62], Small... 

Often the free trimetallasubstituted ligands, e.g. [Co3(CO)9Cm3-E)] (E = P,As), [H2Ru3(CO)9( 3-S)], and [Cos( 6-As)(a4-AsPh)2(CO)i7( 3-As)], are rather difficult to isolate in a pure crystdline state because of their instability under the experimental conditions required for their synthesis. In these cases, such clusters of clusters as [Co,( 4-E)3(CO)24] (Fig. 3-24a), [392] [H6Ru,( 4-S)3(CO)24], [396] and [Co,6( M6-As)2(/<4-As)20u4-AsPh)4(CO)32] (Figure 3-24b) [313] can be formed from their intermolecular dimerization or trimerization reactions via carbon monoxide substitution and directly isolated. 

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