Carbenes carbenoids

The participation of carbene/carbenoid metal complexes in [4S+1C] cycloaddition reactions is very infrequent [81]. In fact, only a few examples involving Fischer carbene complexes have been reported in recent years [82]. A remark-... 

Carbene (Carbenoide), Methoden der Organischen Chemie (Houben Weyl), M. Regitz, Ed. Thieme Verlag Stuttgart, 1989 Vol. E19b, Parts 1 and 2. 

Regitz, M. Carbene (carbenoide), in Methoden der Organischen Chemie (Houben-Weylf, Regitz, M., Ed. Georg Thieme Verlag Stuttgart, 1989, 2. 

Kirmse, W. Carbene carbenoide and carben-analoge. Weinheim Verlag Chemie 1969. 

CARBENIUM CENTER CARBENIUM ION CARBONIUM ION CARBENE Carbenoid,... 

Reactions involving radicals, carbenes, carbenoids, reducing agents and at surfaces 880... 

The third method for alkylidenecycloproparene synthesis provides triafulvene derivatives by way of cycloproparenylidene dimerization166. The reaction is limited in scope by the availability of appropriate carbene (carbenoid) precursors and thus far has provided 98a,b only (equation 22). Attempts to extend the method into the naphthalene series167 by using the known89 naphthalene analogue of 97a provides a very sensitive (air/light) deep red material that is fluorescent and, while uncharacterized, is likely the analogue of 98a. 

W. Kirmse, Carbene, Carbenoide und Carbenanaloge (Verlag Chemie, Weinheim, 1969). 

Kirmse, W. In Carbene, carbenoide and carbenanaloge. Weinheim Verlag Chemie 1969. ) Gilchrist, T. L., Rees, C. W. In Carbenes, nitrenes and arynes. New York Appleton-Century-Crofts 1969. 

Basically, three-membered phosphorus heterocycles should result from [2+l]-cycloadditions involving phosphaalkenes and carbenes, carbenoids,... 

The chemical shifts of 2-lithiated imidazoles in THF-r j range from 195.9 ppm to 216.1 ppm for compounds 51-54 (Figure 13). Simple imidazoles such as 51-53 exist as the ring form even at 20 °C, whereas benzimidazole exists as a mixture of ring 54a and chain 54b, 8q2 158.4 ppm) tautomers. The nature of the lithiated species (carbene, carbenoid, or simple carbanion) is not easily discerned based on the chemical shifts <1997CB1213>. 

The organometallics of this subset are called carbenoids because of their similar reactivity to carbenes. Carbenoids are generated by the reaction of a halide with a metal by halogen-metal exchange. The presumed sequence is shown in the following example. The structure of the organometallic is currently under debate. 

Chloro-l-cyclopropylcyclopropanes 1 were also prepared from 1,1-dichloromethylcyclo-propane, potassium tert-butoxide and alkenes via the corresponding carbene (carbenoid), albeit in low yields. 

The products are 1-bromo-l-chlorocyclopropanes or a mixture of 1-bromo-l-chlorocyclo-propanes with 1,1-dichloro- and 1,1-dibromocyclopropanes, via the corresponding carbenes (carbenoids). 

The generation of these carbenes (carbenoids) and their reactions are described in Houben-Weyl, Vol.4/3, pp252-254 and Vol.E19b, pl692 and 1696. 

Organo-l-organooxycyclopropanes are synthesized via the addition of organo(or-ganooxy)carbene (carbenoid) to an alkene. The alkenes are allowed to react with the carbene (carbenoid) precursor under the following conditions ... 

Numerous reactions of bis(organosulfanyl)carbene (carbenoid) are known (Houben-Weyl, Vol.E19b, pp 1697-1709) but very few l,l-bis(organosulfanyl)cyclopropanes have been prepared by its addition to alkenes (Vol. 4/3, pp 254-255 and Vol. El 9b, pp 1700,1701 and 1708). 

The reaction of chloro(methoxy)methyl tolyl sulfone with a base generates methoxy(4-tosyl)-carbene (carbenoid) which adds to 1,2-dimethoxyethene, straight chain and cyclic enol ethers or arylethenes to give 1-methoxy-l-tosylcyclopropanes. Concentrated (50%) aqueous potassium hydroxide with a catalytic quantity of 18-crown-6 or, in one case, butyllithium, was used as the base (see Houben-Weyl, Vol. El9b, pp 1730-1734). 

Bis(sulfonyl)carbene (carbenoid) is generated photolytically, thermally or catalytically from bis(sulfonyl)diazomethane or from the corresponding phenyliodonium ylide (Houben-Weyl, Vol. E19b, ppl735, 1739-1743). In the latter case only, the carbene reacts with an alkene to form l,l-bis(sulfonyl)cyclopropanes (Houben-Weyl, Vol. E19b, pl743). 

Chloro-l-methyl-2-siloxycyclopropanes are interesting synthetic intermediates as they are easily cleaved to 2-methyl-substituted a,/8-unsaturated aldehydes or ketones. Addition of chloro(methyl)carbene (carbenoid) to trimethylsilyl enol ethers gives l-chloro-l-methyl-2-tri-methylsiloxycyclopropanes 11,70-72 which are usually rearranged without purification, due to their restricted stability. A few examples are given in Table 5 (see also Houben-Weyl, Vol. E19b, p 1516). 

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