Carbon monoxide ring closure

For a review of ring closure reactions with CO, see Mullen, A. in Falbe New Syntheses with Carbon Monoxide, Ref. 767, p. 414. See also Eilbracht, R Hiittmann, G. Deussen, R. Chem. Ber, 1990, 123, 1063, and other papers in this series. 

Cyclopentanones form from CO and double bonds in 1,5-positions (example 43, Table VII). This is a very selective and stereoselective process, the 1,4- or 1,6-positions being not significantly reactive under the same conditions. o-Hydroxyphenylacetylenes also form 5-membered lactones (example 45, Table VII). In some cases ring closure leads to a new nickel-carbon bond into which a new molecule of carbon monoxide can be inserted. This process of alternative insertion of carbon monoxide and other unsaturated ligands can be repeated several times so that complex alicyclic structures can be formed (example 49, Table VII). This... 

Ring closure with formation of heterocyclic derivatives may occur when a nucleophilic function is present in the starting alkene and it is suitably placed for cyclization [30-43]. Both kind of the mechanistic pathways shown in path a of Scheme 3 and in Scheme 4 may operate, as exemplified by Schemes 5-6 (Y = O, NR). Clearly, only in the first case carbon monoxide is incorporated into the heterocyclic ring (cyclocarbonylation). 

A very promising synthesis of /3-lactones has been recently reported, involving the palladium-catalyzed carbonylation reaction of halogeno alcohols. For example, 3-phenyl-2-oxetanone was obtained in 63% yield from 2-phenyl-2-bromoethanol in DMF solution at room temperature under 1 atmosphere pressure of carbon monoxide (equation 115). A proposed mechanism, in which palladium metal inserts into the carbon-halogen bond, followed by insertion of a molecule of carbon monoxide into the carbon-palladium bond and then ring closure, fits kinetics data (80JA4193). 

The same reaction, run in the presence of carbon monoxide, led to the incorporation of an acyl moiety into the 3-position. Ring closure of the ethynylphenol derivative shown in 3.61. in the presence of iodobenzene and carbon monoxide gave the corresponding 3-anisoyl-benzofurane derivative in excellent yield.78... 

The combination of the formation of palladium(II) complexes in the oxidative addition of unsaturated halides onto palladium(O), and the palladium(II) mediated ring closure of olefins allows for the elimination of the oxidant. The ring closure of the methallyl-aniline derivative shown in 3.67. in the presence of /J-bromostyrcnc and a catalytic amount of palladium led to the ring closed - coupled product.84 The ring closure might also be accompanied by other follow-up reactions. 2-Methallyl-anilines were converted for example to indolylacetic acid derivatives in the presence of carbon monoxide.85... 

Synthesis of Heterocycles by Ring Closures with Carbon Monoxide J. Falbe, Newer Methods Prep. Org. Chem., 1971, 6, 193-222. 

An alternative approach to synthesis of this ring system involves insertion of CO into the brominated secondary base (43), by treatment with carbon monoxide, lead tetra-acetate, and triphenylphosphine in tributylamine, the product being the amide (44), reduction of which affords the amine.81 Govadine (42 R1 = R4 = OMe, R2 = R5 = OH, R3 = H) has been synthesized by the conventional ring-closure, with formaldehyde, of the diphenolic base (45), or of its dibenzyl ether, in acid solution.82 Tetrahydroberberines, together with N-benzyltetrahydroisoquinolines, have also been obtained by the electrolytic reduction of 3,4-dihydroisoquinolines of structure (46).83... 

The high ratio of biphenyl to naphthalene may reflect a contribution from a second path, via the primary decomposition product in stepwise loss of carbon dioxide and carbon monoxide, paralleling the reaction sequence known to occur under electron impact. The intermediate species (11) could add to benzene to give biphenyl by subsequent loss of carbon monoxide or fluorenone by ring closure and loss of hydrogen ... 

Photolysis of Me2Sn[Mn(CO)s]2 proceeds with loss of carbon monoxide and four-membered ring closure to form 111, and similar bridging stannylene complexes 112 and 113 are formed by the photochemical treatment of related Fe and Co complexes334. 

Synthesis of heterocycies, by ring closures with carbon monoxide ... 

B. Comils, Hydroformylation , A. MuUen, Reppe Chemistry , and A. Mullen, Ring Closure Reactions with CO, in New Syntheses with Carbon Monoxide , ed. J. Falbe, Springer-Verlag, Berhn, 1980. 

The mechanism proposed by Ddtz involves the insertion of a carbon monoxide into the vinyl carbene complex intermediate with the formation of the vinyl ketene complex (255). Electrocyclic ring closure of (255) leads to the cyclohexadienone complex (252), which is related to the final tenzannulation product by a tautomerizadon when R is hydrogen. The mechanism proposed by Casey differs from that of Ddtz in that the order of the steps involving carbon monoxide insertion and cyclization to the aryl or alkenyl substiment is reversed. < Specifically, the vinyl carbene complex intermediate (248) first undergoes cyclization to the metallacyclohexadiene (249), followed by cartion monoxide insertion to give the intermediate (251), and finally reductive elimination to give cyclohexadienone intermediate (252). At this time the circumstantial evidence favors the intermediacy of vinyl ketene intermediates since they can be trapped from these reactions and isolated where the metal is dispaced from the vinyl ketene functionality however, there is not any evidence which can rule out the alternative mechanism. 

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