Isomunchnone cycloadditions

The results obtained clearly demonstrated that the initially formed rhodium carbenoid prefers to cyclize onto the adjacent imide carbonyl group to form an isomunchnone rather than undergo C-H insertion. The explanation proposed to rationalize this result is that the preferred rhodium carbenoid conformer 79 is the one which avoids unfavorable dipole repulsion between the two carbonyl groups of the imide (i.e. 80). The conformational 

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Maier and Schdffling have extended this intramolecular isomunchnone cycloaddition to a synthesis of fused furans by employing an alkyne dipolarophile. Thus the diazo acetylenes 403 are smoothly converted to furans 404 with catalytic rhodium acetate (Fig. 4.128). 

C. Intramolecular Isomunchnone Cycloaddition Pathway to Lysergic Acid... 

A novel type of heterocyclisation reaction involving the dipolar cycloaddition of jV,A-dialkylamino substituted thioisomunchnones and azodicarboxylates giving 1,2,4-triazine derivatives has been reported. The cycloadduct 26 is initially formed from the isomunchnone 24 and the azodicarboxylate 25, it then undergoes a selective fragmentation to give the 1,2,4-triazine 27 <99TL8675>. 

The isomunchnone dipole approach has been successfully applied to the synthesis of alkaloids ( )-lycopodine. As outlined in Scheme 9, 5-methylcyclohexenone 73 was converted to a-diazo imide 74 in seven steps. The diazo decomposition of 74 with Rh2(pfb)4 in CH2CI2 at 25 °C gives expected tandem ylide cycloaddition products 76 and... 

The 3 + 2-cycloaddition of ring-fused isomunchnones with various dipolarophiles produces predominantly die exo-dipolar adduct exo selectivity could be enhanced by the inclusion of substituents on any position of the fused five-membered ring.112 Dihydropyrimidine-fused isothiomunchnones and isomunchnones (80) undergo intramolecular 1,3-dipolar cycloadditions to form cycloadducts (81) with high regio-and stereo-selectivity (Scheme 28).113 The tandem 1,3-dipolar cycloadditions of 1,3-... 

The first example of a bimolecular 1,3-dipolar cycloaddition between an isomtinchnone and an electron-rich dipolarophile was reported by our group several years ago [27]. The reaction of diethyl ketene acetal and isomtinchnone 9 gave cycloadduct 29 in high yield. Again, only one regioisomer was obtained and the regiochemistry encountered is consistent with cycloaddition involving the HOMO of diethyl ketene acetal and the LUMO of isomunchnone 12 (n = 1). 

Wudl, Padwa, and co-workers found that the Rh(II)-catalyzed 1,3-dipolar cycloaddition of several isomunchnone precursors with C6o readily affords the [3 + 2] cycloadducts, such as ( )-213 (Scheme 1.17).364 On thermolysis, the adducts cleanly regenerated the mesoionic heterocycles, for which they may be used as a repository (Scheme 1.17). When a chiral, racemic isomunchnone precursor was used as starting material, the diastereoisomeric adducts with C60 were formed in unequal amounts which, in the absence of significant steric effects, points toward subtle electronic interactions between the reaction partners.364... 

An interesting example of an intramolecular 1,3-dipolar cycloaddition of an isomunchnone with an unactivated alkene to produce a complex polycyclic compound in one step has been reported <89TL4077 89CB1081>. The isomunchnones derived from the Rh2(OAc)4 catalyzed reaction of acyclic diazoimides 92-96 were found to undergo facile cycloaddition onto the tethered it-bond to provide polycyclic adducts 97-101. A notable feature of this cycloaddition is that only one diastereomer is formed. The relative... 

Lengthening the alkenyl tether by one carbon atom was observed to have no effect on the ability of the isomunchnone to cycloadd across the olefinic jc-bond. This was shown in a study of the cycloaddition behavior of diazoimide 108 which afforded cycloadduct 109 in 86% yield as a single diastereomer <92TL4731>. 

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