Rhodium acetate, reaction with diazo carbonyl

RHODIUM(II) ACETATE-CATALYZED REACTION OF ACETYLENES WITH DIAZO CARBONYL COMPOUNDS ... 

These authors also prepared novel epoxy-bridged cyclooxaalkanones in this process, the carbonyl group always acts as 1,3-dipolarophile, even if one employs ct,(3-unsaturated aldehydes. Thus, reaction of 6/2-16 with aliphatic or aromatic aldehydes 6/2-17 in the presence of catalytic amounts of rhodium acetate gave 6/2-18, regioselectively. With the a, 3-unsaturated aldehydes 6/2-20, only cycloadducts 6/2-21 were obtained using the diazo compound 6/2-19 as substrate (Scheme 6/2.3) [191]. 

Independently, Harwood also demonstrated the role of chiral-templated isomunchnones in 1,3-dipolar cycloaddition reactions. Thus using the rhodium(II)-catalyzed decomposition of diazo carbonyl compounds, Harwood and co-workers explored cycloadditions of isomunchnone derivatives of (5R)- and (55)-phenyloxazin-2,3-dione. Along with the work of Padwa (vide supra), these reactions appear to represent the first examples of chiraUy templated isomunctmone 1,3-dipolar cycloadditions. For example, reaction of 471 under standard rhodium acetate conditions in the presence of NPM affords a mixture of endo-472 and exo-473 adducts (Fig. 4.146). A-Methylmaleimide and DMAD react with 471 similarly. 

In 1989, the Moody s group from UK reported the constmction of seven-membered cyclic ethers (Fig. 3.26) [9] via Rh (Il)-catalyzed intramolecular O-H insertion reaction. With the catalyst of rhodium acetate dimer, the catenulate a-diazo carbonyl substrate containing secondary hydroxyl reacted to obtain seven-membered cyclic ethers under toluene reflux conditions with the yield of 88 %. 

Alkynyl-2-diazo-3-oxobutanoates (391) when treated with catalytic amounts of rhodium(II) acetate were found to produce 1,3-dihydrofuro[3,4-c]furans (392) in good yield. The reaction proceeds by addition of a rhodium-stabilized carbenoid on to the alkynic n bond to give a vinyl carbenoid (393) which subsequently cyclizes on to the neighboring carbonyl group to produce the furan ring <93JOC2l>. 

Decomposition of a-diazo ketoamides 208 in the presence of substituted propiolic esters gives spirocyclic oxiranes 209. The reaction involves intramolecular addition of a rhodium carbenoid onto the oxygen atom of the amide group to yield the carbonyl ylide, which, after 1,4-H-migration, produces a cyclic ketene N,0-acetal 210. The latter further reacts with the activated triple bond of the dipolarophile to form a zwitterionic intermediate and, finally, a spirocycloadduct (Scheme 26) (90JA2037). 

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