Diels-Alder reaction, Metalla

Formation of five-membered carbocycles via a metalla-Diels Alder reaction... 

Thermal Metalla-Diels-Alder Reaction Formation of five-membered carbocycles via a thermal metalla-Diels-Alder reaction is reported in a formal [3+2] cycloaddition of a, 3-unsaturated Fischer carbene complexes 63... 

The reaction can be interpreted by a sequence of carbene ligand metathesis to generate alkenyl carbene complexes 73, followed by the metalla-Diels-Alder reaction with a second diene 72 and reductive fragmentation. 

Metalla-Diels-Alder Reaction via Metal Exchange A significant metal effect on the reactivity of a,(3-unsaturated Fischer carbene complexes is found in the reaction with alkenes and alkynes. Thus, the reaction of electron-poor alkynes with chromium alkenyl(alkoxy)car-benes is usually slow [26], whereas rhodium-catalyzed reactions of chromium alkenyl(methoxy)carbenes 75 with electron-poor alkynes 76 readily afford polysubstituted cyclopentenones 78, 79, and 80 (Scheme 5.17) [27]. Although the reactions proceed with high regioselectivity, the regioselectivity depends on the substituent (R ) of... 

Formation of Five-Membered Heterocycles via a Metalla-Diels-Alder Reaction... 

The reaction of Fischer alkenyl carbene complexes 101 with imines 102 in the presence of a Lewis acid generates pyrroline derivatives 105 as a result of a formal [3+2] cycloaddition via metallacyclic intermediates 103 (Scheme 5.21) [32]. The intermediates 103 are supposed to be formed through a metalla-Diels-Alder reaction. High asymmetric induction is observed in the reaction of chiral alkenyl carbene complexes 101 derived from (—)-8-phenyl-menthol. The major isomer of the trans products 104 can be... 

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