Carbonylation promotions

The presence of a 2-substitutent in 3-phenylazirines (17, R —H in Scheme 21) modifies the mode of reaction with molybdenum carbonyl.47 In contrast to pyrazine formation for (17, R =H see Section V,C,2), the alkenyl azirine (18, Scheme 22) is transformed in excellent yield into 2-phenyl-5-carboxy-methylpyrrole. This product probably arises by intramolecular cyclization within an intermediate dienylnitrene intermediate, and related reactions have been devised to synthesize isoxazoles (see Section IV,E,2) and pyrazoles (see Section IV,D,1).47 The molybdenum carbonyl-promoted formation of 2,5-disubstituted pyrroles47 has analogy in uncatalyzed thermal, but not photochemical decomposition of 3-phenyl-2//-azirine 2-acrylate.49... 

Representative Procedure for Carbonyl Promoted Clycosylation with Cl-Hemiacetal Donors Using Trichloroacetic Anhydride [152]... 

As indicated in Chapter 8, the production of alkanes, as by-products, frequently accompanies the two-phase metal carbonyl promoted carbonylation of haloalkanes. In the case of the cobalt carbonyl mediated reactions, it has been assumed that both the reductive dehalogenation reactions and the carbonylation reactions proceed via a common initial nucleophilic substitution reaction and that a base-catalysed anionic (or radical) cleavage of the metal-alkyl bond is in competition with the carbonylation step [l]. Although such a mechanism is not entirely satisfactory, there is no evidence for any other intermediate metal carbonyl species. 

Desulphurization of thiols has been accomplished in high yield under phase-transfer conditions using tri-iron dodecacarbonyl (or dicobalt octacarbonyl). The mechanism proposed for the formation of the alkanes and the dialkyl sulphide byproducts involves a one electron transfer to the thiol from the initially formed quaternary ammonium hydridoiron polycarbonyl ion pair [14], Similar one electron transfers have been postulated for the key step in the cobalt carbonyl promoted reactions, which tend to give slightly higher yields of the alkanes (Table 11.18). 

In 1987, Nitta reported the formation of an unexpected vinylketene complex from the reaction of an azido-substituted cyclopropene with diiron nonacarbonyl.104 They had previously investigated the chemical behavior of the complexed nitrene intermediates that result from the reaction of organic azides and iron carbonyls113 and were interested in replicating the thermal isomerization of 3-azido-l,2,3-triphenylcyclopropene (163) into 4,5,6-triphenyl-l,2,3-triazine using a metal carbonyl-promoted re-... 

Since the pioneering work by Sarel and co-workers on the iron carbonyl promoted transformation of vinylcyclopropanes and related compounds [1], a variety of transition metal complexes have been examined to achieve effective activation of the vinylcyclopropane-cyclopentene rearrangement which usually requires pyrolytic conditions. These reactions have been applied to natural product synthesis in some cases and have already been reviewed in several excellent articles [2-4]. 

Reactions Involving Carbonylations Promoted by Ruthenium Complexes... 

The iron carbonyl-promoted [3 + 4] cycloaddition of bromo-ketones to. 1,3-dienes provides a convenient way, via 2-oxyallyIs, of synthesizing tropones and hence thujaplicins. The synthesis of nezukone (154 X = H)253 has been reported from a,a,a, a -tetrabromoacetone and 3-isopropylfuran. Similarly, from 2-isopropylfuran, /3-thujaplicin (154 X = OH) has been synthesized from the corresponding tropone by known methods, and a-thujaplicin synthesis requires isopropyl substitution in the ketone moiety.254 Karahanaenone (155) is a minor product from pyrolysis of the benzoate (156).149... 

Hayakawa, Y Takaya, H., Makino, S., Ha-yakawa, N., and Noyori, R Synthesis of, 3(2II)-furanones by the iron carbonyl-promoted cyelocoupling reaction of o,a -dibromo ketones and carboxyamidcs. A convenient route to muscarines. Bull. Chem. Soc. Jpn.. 50, 1990, 1977. 

The iron carbonyl-promoted reaction of secondary dibromo ketones and an amide produces 3(2//)-fu-ranone derivatives (69) (equation 36). This cyclocoupling reaction has some useful applications, such as the synthesis of a muscarine analog (70) from furanone (71) (equation 57). Reaction of the dibromo ketone (72) with A(-methylpyrrolidinone results in formation of the aminofuranone (73) via an intramolecular deamination (equation 58). 

Boc-activation of the benzamide carbonyl promotes facile cleavage from the resin with methoxide. 

Alkyl halides are usually considered to be less suitable for double carbonylation because of the possibility of the direct reaction of alkyl halides with nucleophiles and of instability of alkyl-transition metal complexes involved in the catalytic process. However, allylic halides were found amenable to double carbonylation promoted by zerovalent palladium complex. It is well known that allylic halides undergo ready oxidative addition with a Pd(0) species to produce Tj -allylpalladium halide complexes. Thus, it was reasoned that the double carbonylation process might be realized if CO insertion into the aUyl-palladium bond proceeds before attack of amine on the 17 -allylpaUadium halide takes place. On the basis of fundamental studies on the behavior of i7 -allylpalladium halide complexes with CO and secondary amines, double carbonylation processes of substituted aUyl halides to give a-keto amides in high yields have recently been achieved (Eqs. 15 and... 

Nickel carbonyl-promoted addition of haloacetonitriles to benzaldehyde via similar intermediates was mentioned briefly as the unpublished results by Yoshisato, E. Abe, T. Murai, S. Sonoda, N. Tsutsumi, S. in M. Ryang, Organomet. Chem. Rev. A. 1970, 5, 67. 

Butanol is prepared commercially by the iron carbonyl-promoted hydro-xymethylation of propylene (Reppe and Vetter, 1953). Iron pentacarbonyl and a tertiary amine serve as a good catalyst system. The active species has been shown to be HFe(CO)4 formed from the metal carbonyl and hydroxide ion (Wada and Matsuda, 1974). 

The iron carbonyl-promoted cyclocoupling reaction of polybromo-ketones and unsaturated substrates provides a powerful tool for the synthesis of five- and seven-membered carbocycles. The intramolecular version of this reaction has now been reported for the synthesis of polycyclic terpenes. Reaction of the dibromo-ketone (54), obtained from geraniol, with [Fe2(CO)9] in benzene under pressure gives, in 70% yield, a Cio fraction, the major component (54%) of which is camphor. The other major component (20%) is dihydrocarvone (56). Other cyclic terpenes can be synthesized by similar reactions. 

General Methods.—Among the methods now available for the direct synthesis of cyclopentanes via a [3 + 2] combination of carbon units, the iron carbonyl-promoted coupling between a,a -dibromo-ketones and olefins has always seemed especially attractive. This year sees the publication of a timely review by Noyori, the pioneer in this field, together with a report of the intramolecular version of the method [e.g. (43) -> (44) and (45) - (46)]. The palladium... 

Noyori et a/. >have reported an intramolecular variant of their iron carbonyl-promoted [4+3] coupling of polybromoketones with dienes [e.g. (204 -+ (205)]. 

The iron carbonyl promoted cyclocarbonylation of 2-hydroxy-a, -diynes to give (i) -cyclopentadienone)iron tricarbonyl complexes such as (30) has been described i. ... 

RhCl(PPh8)a] catalyses similar cyclizations of 4,4-disubstituted 1,6-dienes to methylene cyclopentanes. The stereochemistry of iron-carbonyl-promoted ring-openings may be predicted by Frontier Molecular Orbital Theory.A mechanism involving initial oxidative-addition to give an acylrhodium(iii) hydride intermediate has been proposed to explain the Rh f-catalysed cyclization reaction (13) - alkyl substituents in either the 2 or 5 positions substantially... 

General Methods.—The direct synthesis of cyclopentanes by a [3 + 2] combination of carbon units has been the goal of many synthetic chemists in the past decade. This year has seen the publication of several new routes to cyclopentanes which fall into this category. A particularly facile method uses the Michael addition of the vinyl carbanion (45) to double bonds as a key stage,whereas Hayakawa et al. have shown that the iron carbonyl-promoted reactions of a,a -dibromo-ketones and alkenes can provide an expeditious route to certain substituted cyclopentanones [e.g. (46) — (47)]. Two further examples of the... 

Noyori et alS have reported their studies of the iron carbonyl-promoted [4 + 3] cyclo-coupling of polybromo-ketones with 1,3-dienes as a method of preparing cyclohept-4-enones, and in a subsequent paper describe methodology for converting these products into a number of troponoid compounds/ ... 

Metal carbonyl promoted rearrangement of phenyl-cyclopropenes to naphthols... 

Metal Carbonyl Promoted Rearrangement of Phenylcyclopropenes to Naphthols... 

In 1987, Semmelhack et al. [21] published a paper concerning metal carbonyl promoted rearrangement of phenylcyclopropenes to naphthols (Scheme 17.26), which can also be classified as a [5+1] cycloaddition. The reaction can be promoted by a stoichiometric amount of Cr(CO)s or Mo (CO)5, or a catalytic amount of Mo(CO)5 but with lower yields and rates. With respect to the substrate scope, the authors found that the substituent was crucial only when was methoxy or hydrogen, the desired naphthol products can be obtained in good yields (35-78%). Otherwise, low... 

The synthesis of scopine illustrates a novel general synthesis of tropane alkaloids based on the iron carbonyl promoted cyclocoupling reaction between OjO -dibromo ketones and 1,3-dienes leading to 4-cycloheptenones. Tetrabromoacetone provides the starting three-carbon unit, serving as a synthetic equivalent of the unsubstituted oxyallyl species (i) which is trapped using N-carbethoxypyrrole. ... 

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