Hemicaronic aldehyde

Reaction of methyl 4-bromo-2-methoxycarbonyl-4-methylpent-2-enoate (24) with 3.2 equivalents of sodium cyanide in dimethyl sulfoxide at 20 °C for 3 hours leads to the formation of dimethyl 3-cyano-2,2-dimethylcyclopropane-l,l-dicarboxylate (25) which is readily de-methoxycarbonylated to give tra 5-3-cyano-2,2-dimethylcyclopropanecarboxylic acid (26) in 67% overall yield. This compound can be conveniently transformed into chrysanthemic acid and hemicaronic aldehyde. ... 

This method was used in the stereoselective synthesis of cis- and /ran -hemicaronic aldehydes 9 which were prepared in high enantiomeric purity starting from optically active sorbic aldehyde diene tricarbonyliron complex 6 via Wittig olefination, diazo ester cyclopropanation (copper powder), and further conversion with release of the cyclopropane from the complex and ozonolysis. ... 

Several other examples of uncomplexed double-bond cyclopropanation within tricarbonyliron complexes and decomplexation without ring opening have been reported. These include alternative stereospecific pathways to hemicaronic aldehydes. 

Methyl (R)-/rara-4,5-0-isopropylidene-4,5-dihydroxy-2-pentenoate and isopropylidene triphenylphosphorane furnish the (l/ ,2/ )-tra .s-cyclopropane derivative 40 as the major diastereomer (d.r. 93 7) with a 60% yield87. Starting with the corresponding ethyl ester, a d.r. of >98 2 can be obtained. Purification of these intermediates by recrystallization, followed by oxidative degradation of the inducing dioxolane moiety, leads to methyl (/ ,/ )-2-formyl-3,3-dimethylcy-clopropanecarboxylate [(lR.2/ )-hemicaronic aldehyde] in enantiomerically pure form. 

When isopropylidene triphenylphosphorane is added to the (1 /(.2,S)-norephcdrinc based unsaturated oxazolidine 41 the cyclopropane derivative is formed as a single diastereomer in 60% yield88. Removal of the heterocyclic auxiliary affords optically pure methyl (R,R)-2-formyl-3,3-dimethylcyclopropanecarboxylate [(1 / ,2/ )-hemicaronic aldehyde, 42],... 

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