Chromium , pentacarbonyl methoxy

Structural analogues of the /]4-vinylketene E were isolated by Wulff, Rudler and Moser [15]. The enaminoketene complex 11 was obtained from an intramolecular reaction of the chromium pentacarbonyl carbene complex 10. The silyl vinylketene 13 was isolated from the reaction of the methoxy(phenyl)-carbene chromium complex 1 and a silyl-substituted phenylacetylene 12, and -in contrast to alkene carbene complex 7 - gave the benzannulation product 14 after heating to 165 °C in acetonitrile (Scheme 6). The last step of the benzannulation reaction is the tautomerisation of the /]4-cyclohexadienone F to afford the phenol product G. The existence of such an intermediate and its capacity to undergo a subsequent step was validated by Wulff, who synthesised an... 

Triethylamine (8) Ethanamine, N,N-diethyl- (9) (121-44-8) Pentacarbonyl[phenyl(methoxy)chromium]carbene Chromium, pentacarbonyl(a-methoxybenzylidene)- (8) ... 

Simple alkenes, norbomene and styrene do not undergo cyclopropanation or insertion reactions with cyclopropyl(methoxy)carbene chromium pentacarbonyl complex. However, the conjugated 1-vinylcyclopentene is cyclopropanated under the reaction conditions at the terminal double bond, affording an isomeric mixture (trans cis = 40 60), in 66% yield (equation 72). 

The rearrangement exhibits some stereochemical preference for c/s-vinyl carbene complex (with respect to the metal) compared to the //ww-isomer. Thus, 2-methyl-2-m-vinyl cyclopropyl (methoxy) carbene chromium pentacarbonyl rearranges to 5-methyl-5-vinyl-2-methoxycyclopentenone approximately 4 times faster (THF, 52 °Q than the trans-isomer, which in turn rearranges faster than phenyl derivatives. This suggests that vinyl complexes undergo initial Cope-type rearrangement to form metallacycloheptadienes, which then rearrange to jt-allyl complexes. Subsequent CO insertion and reductive elimination leads to the vinylcyclopentenones (equation 89)150. 

Methyl) (methoxy)carbene] jentacarbonyl chromium(O) Chromium, pentacarbonyl(1-methoxyethylidene)-, (8) Chromium, pentacarbonyl(1-methoxyethylidene)-, (OC-6-21)-, (9) (20540-69-6)... 

A reaction between pentacarbonyl[methoxy(2,6-dimethoxyphenyl) methylene]chromium(0) and pent-4-yn-l-ol provides direct access to the functionalized tetrahydropyran-2-one 1005 the best yield is obtained via thermal heating of the two starting materials in THF (Equation 395) <2000TL9323>. 

Charge the first flame dried and argon flushed two-necked flask with pentacarbonyl-(methoxy(4-pentenyl)carbene)chromium(0). 

The first X-ray crystal structure determination, carried out by Mills in cooperation with us 31) on pentacarbonyl[methoxy (phenyl) carbene ]-chromium(0), confirmed our originally postulated bonding concept. According to this concept, the carbene carbon atom is sp1 hybridized. It should therefore possess an empty p-orbital and be electron-deficient. 

Fig. 2. The structure of pentacarbonyl [methoxy(phenyl)carbene]chromium (0) bond lengths in angstroms.

Fig. 4. Reactions of pentacarbonyl[methoxy(methyl)carbene]chromium(0) with tertiary phosphines.

Fig. 6. Hypothesis concerning the course of the reaction during the treatment of pentacarbonyl[methoxy(phenyl)carbene]chromium(0) with JV-vinyl-2-pyrrolidones under a CO pressure of 150 atm.

As mentioned earlier, the carbene ligand in our complexes shows nucleophilic character with respect to the metal fragment. Therefore, we decided to combine it with an electrophilic carbene. For this purpose we treated pentacarbonyl[methoxy(phenyl)carbene]chromium(0) with phenyl(tri-chloromethyl) mercury (85). Compounds of this kind have been studied intensively by Seyferth et al. (86) and are known as a source of dihalogeno-carbenes. The carbene complex reacted with the carbenoid compound at... 

K. H. Dotz, Synthesis of the Naphthol Skeleton from Pentacarbonyl[methoxy(phenyl)-carbene]chromium(0) and Tolane, Angew. Chem. Int. Ed. Engl. 14, 644-645 (1975). 

Dotz, K. H. Synthesis of the naphthol skeleton from pentacarbonyl[methoxy(phenyl)carbene]chromium(0) and tolan. Angew. Chem. 1975, 87, 672-673. 

The reaction of pentacarbonyl[methoxy(phenyl)carbene]chromium(0) with vinyl ethers gives 1-methoxy-l-phenylethene as the main product. If these substrates are allowed to react in the presence of carbon monoxide under pressure, the corresponding cyclopropanes are formed in good yield. 

Procedure A A solution of pentacarbonyl[methoxy(cyclopropyl)carbene]chromium(0) (0.276 g, 100 mmol) and an alkene (2.00 mmol) in THE (20 mL) was added dropwise via a syringe pump over a period of 5 h to refluxing THE (tOOmL) under N2. 

Pentacarbonyl[methoxy(phenyl)carbene]chromium(0) reacts regioselectively across the 4,5-double bond of electrophilic conjugated dienes. The reactions run at a much slower rate than those with electrophilic alkenes, e.g. formation of 6, 7 and 8-10. The diastereomer with the methoxy group cis to the olefinic moiety is largely favored (85 15). Double adducts are only formed as minor side products, but they become the major product in the case of (E,E)-7V,iV-dimethylhexadienamide. ... 

In MeOD solutions, in the presence of catalytic amounts of sodium methanolate, pentacarbonyl[methoxy(methyl)carbene]chromium(0) exchanges all hydrogen atoms of the methyl group for deuterium. Analogous molybdenum and tungsten complexes react in the same manner. 

In an interesting and novel organometallic approach to monocyclic and bicyclic p-lactam synthesis, it has been shown that pentacarbonyl(methoxy-methyl)chromium complexes will add to imines under sunlight irradiation (Scheme 38). ... 

Another route to vinylcarbene C-glycosides is based on a TiCl4-assisted aldol condensation of pentacarbonyl[(methoxy)methylcarbene]chromium (229) and formyl glycosides 230-232. This reaction is trans-selective and affords sugar carbene complexes 233-235 in good yields (Scheme 11.53) [111]. 

The inherent plane of chirality in the metal carbene-modified cyclophane 45 was also tested in the benzannulation reaction as a source for stereoselectivity [48]. The racemic pentacarbonyl(4-[2.2]metacyclophanyl(methoxy)carbene)-chromium 45 reacts with 3,3-dimethyl-1-butyne to give a single diastereomer of naphthalenophane complex 46 in 50% yield the sterically less demanding 3-hexyne affords a 2 1 mixture of two diastereomers (Scheme 30). These moderate diastereomeric ratios indicate that [2.2]metacyclophanes do not serve as efficient chiral tools in the benzannulation reaction. 

Pentacarbonyl[phenyl(methoxy)carbene]chromium was prepared by the checkers in 75% yield according to the literature Hegedus, L. S. McGuire, M. A. Schultze, L. M. Org. Synth. 1987, 65,140. This material was stored under nitrogen at -30°C and purified immediately prior to use by filtration through a plug of Celite (hexane solvent). If the chromium carbene is purchased from Aldrich Chemical Company, Inc., the submitters found it was only 65% pure based on capillary GLC analysis. 

Methyl)(methoxy)carbene]pentacarbonyl chromium(O) Chromium,... 

---