Alkene derivatives diastereoselective cyclic reactions

The dicarboxylation of cyclic alkenes is a useful reaction. Only cxo-methyl-7-oxabicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylate (121) was prepared from the cyclic alkene 120 using Pd on carbon and CuCl in MeOH at room temperature with high diastereoselectivity [89]. Methyl nitrite 37 is used for efficient oxidative carbonylation of alkenes to produce the succinate derivatives 122 [la,90]. It was claimed that the... 

Padwa and Prein (105,106) applied chiral, but racemic, isomiinchnone dipoles in diastereoselective 1,3-dipolar cycloadditions. The carbonyl ylide related isomiinch-none derivative rac-70 was obtained from the rhodium-catalyzed cyclization of diazo-derivative rac-69 (Scheme 12.24) (105). The reactions of the in situ formed dipole with a series of alkenes was described and in particular the reaction with maleic acid derivatives 71a-c gave rise to reaction with high selectivities. The tetracyclic products 72a-c were all obtained in good yield with high endo/ exo and diastereofacial selectivities. In another paper by the same authors, the reactions of racemic isomilnchnones having an exo-cyclic chirality was described (106). 

The reaction proceeds via a tandem Michael addition-HBr elimination in which the carbanion (48) is the key intermediate to produce cyclopropanation. The success of the method depends from the correct addition of (46) to the basic solution of the alkenes (47). In fact, it is important to add bromonitromethane in several fractions in order to avoid its decomposition (that can happen under basic conditions). The cyclopropanation proceeds in good to excellent yields (75-96%) with a variety of substrates, but with moderate diastereoselectivity. The procedure works well even with cyclic alkenes, such as 7V-alkylmaleimides, with the exclusive formation of exocyclopropane derivatives. 

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