Rhodium carboxylates diazo compound decomposition catalysts

Diazo Compounds Decomposition with Chiral Rhodium Catalysts. The first chiral rhodium catalyzed asymmetric cyclopropanation was reported in 1989 (75). Structures of the catalysts were based on the framework of dirhodium(II) tetrakis(carboxylate) 1 with the carboxylate ligands replaced with... 

Electron-withdrawing substituents generally increase diazo compounds stability toward decomposition. Dicarbonyl diazomethane, which bears two carbonyl groups flanking the diazomethane carbon, are more stable than diazo compounds with only one carbonyl substituent. In general, metal catalysed decomposition of dicarbonyl diazomethane requires higher temperature than does monocarbonyl substituted diazomethane. As indicated before, rhodium(II) carboxylates are the most active catalysts for diazo decomposition. With dicarbonyl diazomethane, the rhodium(II) carboxylate-promoted cyclopropanation process can also be carried out under ambient conditions to afford a high yield of products. 

Binuclear Rhodium(ll) Catalysts. Soon after the first report of dirhodium(ll) carboxylates 1 (Scheme 1) as effective catalysts for diazo decomposition in 1973 (21), this type of complex was discovered to actively catalyze cyclopropanation (22). Comparison of relative reactivity and stereoselectivity of catalyst 1 (R = CHs) and a stoichiometric carbene complex of (COsWCHPh for cyclopropanation of alkenes with phenyldiazomethane showed rhodium carbene involvement in the rhodium-catalyzed cyclopropanation (23). Catalyst 1 (R = CH3) also demonstrated improvement of cyclopropane production can be achieved by decreasing the available concentration of the diazo compound with a slow addition method (24). 

Allyldiethylamine behaves similarly, but the yields are low since neither the starting amine nor the products are stable to the reaction conditions. For the efficiency of the cyclopropanation of the allylic systems under discussion, a comparison can be made between the triplet-sensitized photochemical reaction and the process carried out in the presence of copper or rhodium catalysts whereas with allyl halides and allyl ethers, the transition metal catalyzed reaction often produces higher yields (especially if tetraacetatodirhodium is used), the photochemical variant is the method of choice for allyl sulfides. The catalysts react with allyl sulfides (and with allyl selenides and allylamines, for that matter) exclusively via the ylide pathway (see Section 1.2.1.2.4.2.6.3.3. and Houben-Weyl, Vol. E19b, pll30). It should also be noted that the purely thermal decomposition of dimethyl diazomalonate in allyl sulfides produces no cyclopropane, but only the ylide-derived product in high yield.Very few cyclopropanes have been synthesized by photolysis of other diazocarbonyl compounds than a-diazo esters and a-diazo ketones, although this should not be impossible in several cases (e.g. a-diazo aldehydes, a-diazocarboxamides). Irradiation of a-diazo-a-(4-nitrophenyl)acetic acid in a mixture of 2-methylbut-2-ene and methanol gave mainly l-(4-nitrophenyl)-2,2,3-trimethylcyclo-propane-1-carboxylic acid (19, 71%) in addition to some O-H insertion product (10%). ... 

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