Substituted Fischer carbenes

From Alkyl-Substituted Fischer Carbene Complexes. 23... 

Recently, Aumann et al. reported that rhodium catalysts enhance the reactivity of 3-dialkylamino-substituted Fischer carbene complexes 72 to undergo insertion with enynes 73 and subsequent formation of 4-alkenyl-substituted 5-dialkylamino-2-ethoxycyclopentadienes 75 via the transmetallated carbene intermediate 74 (Scheme 15, Table 2) [73]. It is not obvious whether this transformation is also applicable to complexes of type 72 with substituents other than phenyl in the 3-position. One alkyne 73, with a methoxymethyl group instead of the alkenyl or phenyl, i.e., propargyl methyl ether, was also successfully applied [73]. 

Diels-Alder additions to 17-19 parallel the known Diels-Alder additions to vinyl substituted Fischer carbene complexes (34). It appears that both M(CO)5 carbene moieties, where M is Cr or W, and (ferra-/3-diketonato)BF2 substituents can activate C=C double bonds toward Diels-Alder additions. 

The reaction of deprotonated 2-aminophenol 115 with an alkynyl-substituted Fischer carbene 277 gave a cyclic complex 279 in 40% yield, most probably via an intermediate adduct 278 (X = 0). On the other hand, complex 280, obtained from 115 and 277 without base, was heated in tetrahydrofuran to afford benzoxazepine derivative 281 (38%) and benzoxacinone 282 (36%) with reverse regiochemistry (Scheme 49) <2003CEJ4943>. 

The relatively acidic a hydrogens of amino- and alkoxy-substituted Fischer carbenes are readily removed... 

Alkene- and alkyne-substituted Fischer carbenes participate as dienophiles in Diels-Alder reactions. The conditions are usually mild and the reaction proceeds smoothly at room temperature. Similar isomeric ratio and rate acceleration is observed to that of Lewis acid-promoted Diels-Alder reactions between methyl acrylates and dienes when compared to the uncatalyzed reactions. The reactions are endo-selective. Asymmetric Diels-Alder reactions are... 

Thermal reaction of alkoxy-substituted Fischer carbenes of group 6 metals with alkynes has been applied to the... 

The benzannnlation reaction of aryl- and alkenyl-substituted Fischer carbenes with alkynes has been used... 

Thiols and thiolates react with ( -substituted Fischer carbenes in an analogous manner, as shown in equation 10.27,4S... 

Oxidative decomposition of cyclopropyl-substituted Fischer-carbene complexes with pyridin-ium iV-oxide stereoselectively leads to cyclopropylcarboxylates. ... 

Amino-substituted Fischer carbene complexes can also be prepared from isocyanide complexes. This synthesis is less common than the synthesis of alkoxy-substituted carbenes because there are fewer appropriate isocyanide complexes to use as reactants than there are carbonyl complexes, and isocyanide ligands are less electrophilic. Thus, this reaction sequence has often been conducted intramolecularly to promote attack on the isocyanide ligand instead of an ancillary carbonyl group. An intramolecular example of the synthesis of an amino-substituted carbene by attack of an isocyanide ligand is shown in Equation 13.3, ... 

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