Rhodium cyclobutanones

Cyclopropanes 13 have been prepared from a NHC-rhodium catalysed decarbonylation of cyclobutanones 11 (Scheme 5.4) [6]. The isolated complex 12... 

As invented by Wender,196,197 a variant of the second transformation can take place if the alkene partner is substituted by a participating group such as a strained cyclopropyl or a cyclobutanone (in the case of a 1,6-diene).198 The whole process, which mainly relies on the use of rhodium or ruthenium complexes,1 9 results in the formal... 

A rhodium(I)-.A-heterocyclic carbene complex has brought about a chemoselective decarbonylation, converting a cyclobutanone to the corresponding cyclopropane, while leaving an aldehydic substituent untouched.336... 

Lawlor, M. D., Lee, T. W., Danheiser, R. L. Rhodium-Catalyzed Rearrangement of a-Diazo Thiol Esters to Thio-Substituted Ketenes. Application in the Synthesis of Cyclobutanones, Cyclobutenones, and 3-Lactams. J. Org. Chem. 2000, 65, 4375-4384. 

Ordinary cyclic mono-ketones were also decarbonylated by the action of a stoichiometric amount of RhCl(PPh3)3 [46, 47]. Treatment of cyclobutanone with (Ph3P)3RhCl results in decarbonylation to afford the corresponding cyclopropane together with the rhodium carbonyl complex 28. Insertion of rhodium... 

Cyclobutanones are catalytically decarbonylated by rhodium [46,47]. Appropriate choice of the catalyst system leads to the selective formation of either a cyclopropane or an alkene. 

When cyclobutanone is treated under dihydrogen with a catalytic amount of a rhodium(I) complex containing a bidentate diphosphine ligand, the ring opened alcohol 89 is produced in goodyield [46,47]. The oxidative addition intermediate 87 is hydrogenated to give aldehyde 88, which is further reduced to the alcohol 89. 

The reaction of a spiro cyclobutanone equipped with a second four-mem-bered ring (97) catalyzed by [Rh(dppp)2]Cl gives rise to 2-cyclohexenone 98 [117]. Rhodium successively cleaves the two C-C bonds of 97, the first by oxidative addition and the second by (3-carbon elimination. 

The other example of a rhodium migration was discovered when 3-substituted-3-(2-hydroxyphenyl)cyclobutanones were subjected to rhodium-catalyzed conditions (Scheme 17) [76], The reaction generates dihydrocoumarin derivatives in high... 

Murakami s group has developed various rhodium-catalyzed C—C bond cleavages of small rings. Recently, they reported rhodium-catalyzed carbonylation reactions of spiropentanes involving two different types of C—C bond cleavage processes (Equation 11.43) [85]. The reaction allows for the synthesis of a series of 3-methylcyclopent-2-enones, one of which has been utilized as an intermediate in the concise synthesis of ( )- 3-cuparenone. Another example is the rhodium-catalyzed intramolecular olefin insertion of 3-(o-styryl)cyclobutanone to generate... 

Wender et al. demonstrated the rhodium-catalyzed intramolecular [6 + 2]-cycloaddition of 2-(l,6-dienyl)-cyclobutanones 158 (Scheme 55).130 The five-mem-bered heterocycles 159 were synthesized using substrates 158, which had a nitrogen or oxygen atom in a tether moiety. The reaction proceeds through formation of the five-membered metallacycle 160 and subsequent /Tcarbon elimination (de-carborhodation), leading to the nine-membered metallacycle 161, which produces 159 upon reductive elimination of Rh. 

All efforts to affect the requisite cyclization however proved futile. When rhodium acetate in benzene was used as a catalyst, C—H insertion of the resulting carbenoid occurred to furnish cyclobutanone 285, which was not isolated, but underwent ring opening to yield tetrahydro-P-carboline 286. The use of catalytic copper(I) triflate, protic add catalysis, and photolysis conditions were also explored, but the desired product was not obtained. 

Rhodium(III)-promoted intramolecular hydroarylation or amidoarylation of iV- 3-[(but-3-yn-l-yl)oxy]phenyl acetamides are conditions-controUable to afford chromans or heterocyclic-fiised chromans,respectively (14CC7306). A different rhodium catalyst was applied to the synthesis of ring-fused chromans through decarbonylative alkyne insertion of 2-[(but-3-yn-l-yl)oxy] benzo cyclobutanones (Scheme 29) (14AGE1674). 

A rhodium-catalyzed cascade reaction of a cyclobutanone with an electron-deficient alkene ... 

Carbonylation and decarbonylation reactions of alkyl complexes in catalytic cycles have been reviewed . A full account of the carbonylation and homologation of formic and other carboxylic acid esters catalysed by Ru/CO/I systems at 200 C and 150-200 atm CO/H2 has appeared. In a novel reaction, cyclobutanones are converted to disiloxycyclopentenes with hydrosilane and CO in the presence of cobalt carbonyl (reaction 4) . The oxidative addition of Mel to [Rh(CO)2l2] in aprotic solvents (MeOH, CHCI3, THF, MeOAc), the rate determining step in carbonylation of methyl acetate and methyl halides, is promoted by iodides, such as Bu jN+I", and bases (eg 1-methylimidazole) . A further kinetic study of rhodium catalysed methanol carbonylation has appeared . The carbonylation of methanol by catalysts prepared by deposition of Rh complexes on silica alumina or zeolites is comparable with the homogeneous analogue . 

Murakami, M. Tsuruta, T Ito, Y. Lactone Formation by Rhodium-Catalyzed C-C Bond Cleavage of Cyclobutanone. Angew. Chem., bit Ed. 2000,39,2484-2486. 

Matsuda T, Shigeno M, Murakami M (2007) Asymmetric synthesis of 3,4-dihydrocoumaiins by rhodium-catalyzed reaction of 3-(2-hydroxyphenyl)cyclobutanones. J Am Chem Soc 129 (40) 12086-12087. doi 10.1021/ja075141g... 

Transition metal alkoxides of tert-cyclobutanols undergo ring opening by P-carbon elimination to generate ketones that are metalated at the y-position these can be utilized in many functionalization reactions. Palladium, rhodium, and nickel have been the most studied metals in these transformations. Useful transition metal cyclobutanolates are generated from either cyclobutanones or cyclobutanols. 

Monosubstituted cyclobutanones reacted with arylboronic acids in the presence of a Rh(I)-P(f-Bu)3 catalyst to afford butyrophenone derivatives by the addition of an arylrhodium(I) species to the carbonyl group, followed by ring opening of the resulting rhodium(I) cyclobutanolate by P-carbon elimination... 

Rhodium-catalyzed arylation of 2-(2-alkynylphenyl)cyclobutanone 39 proceeded with site-selective P-carbon elimination of the benzylic carbon to afford the seven-membered ring ketone 40 (Scheme 3.19) [31]. 

The reactions of a 3-monosubstituted cyclobutanone with alcohols and an amine were catalyzed by rhodium-dip hosphine complexes to produce esters and an amide, respectively (Scheme 3.20) [32]. 

Asymmetric synthesis of 3,4-dihydrocoumarin 41 was achieved by rhodium(I) catalyzed intramolecular reaction of phenol-substituted cydobutanone 42 (Scheme 3.21) [33]. When the reaction of 3,3-disubstituted cyclobutanones was performed in the presence of electron-deficient alkenes, the arylrhodium species generated via 1,4-rhodium shift underwent addition to the alkenes, providing 5-alkylated dihydrocoumarins (Scheme 3.22). 

Similarly to cyclopropanes, four-membered carbocyclic compounds undergo oxidative addition to low-valent transition metals to form five-membered metallacycles. Rhodium(I) inserts into C-C bonds next to the carbonyl group of ketones to form a rhodacycloalkanone species [49]. The C-C bond of cyclobutanone was cleaved, even at room temperature, by oxidative addition to a rhodium(I) complex having a PBP pincer ligand [50]. In the case of cyclobutanone 70, catalytic decarbonylation was possible and afforded the alkene 71 and cyclopropane 72 (Scheme 3.40). 

Control experiments using a rhodium -NHC (NHC = iV-heterocyclic car-bene) complex catalyst revealed that cyclobutanones were more susceptible to decarbonylation than aldehydes (Scheme 3.41) [51]. 

Under H2, the rhodium(I)-catalyzed C-C bond cleavage reaction of cyclobutanone 73 afforded ring-opened alcohol 74 (Scheme 3.42). Based on the state-of-the-art knowledge of cyclobutanone/cyclobutanol chemistry, we may assume that hydrogenolysis proceeds through ring opening of rhodium cyclobutanolates by P-carbon elimination. 

Successive cleavage of C-C bonds occurred with spirocyclic cyclobutanone 75 (Scheme 3.43) [52]. First, rhodium(1) underwent insertion into the cyclobutanone C-C bond to generate a five-membered cyclic acylrhodium intermediate. 

The rhodium-catalyzed successive C-C/C-O bond cleavage reaction of a cyclobutanone 77 containing a phenoxymethyl side chain was affected by the employed bidentate diphosphine ligand (Scheme 3.44) [53]. In the presence of [Rh(nbd)(dppe)]PF 5 (nbd, norborna-2,5-diene dppe, l,2-bis(diphenylphos-phino)ethane) (5 mol%) and diphenylacetylene (20 mol%), cyclobutanone 77 was transformed into the alkenoic ester 78 in 88% yield via C-C bond cleavage, P-oxygen elimination, and reductive elimination. In contrast, the [Rh(nbd)(dppp)]PFg-catalyzed (dppp, l,3-bis(diphenylphosphino)propane) reaction afforded cyclopentanone 79 in 81% yield through a rhodacyclohexanone species that was formed by 6-endo cyclization. The reaction of the cyclobutanone 77 catalyzed by [Rh(nbd)(dppb)]PFg (dppb, l,4-bis(diphenylphosphino)butane) led to exclusive formation of cyclopropane 80 via decarbonylation. 

Intramolecular insertion reactions of alkenes into cyclobutanone C-C bonds were catalyzed by cationic rhodium(l) complexes (Scheme 3.45) [54]. 3-(2-Vinylphenyl)cyclobutanone 81 were transformed into ketone 82 having a bicyclo[3.2.1] skeleton. 

Murakami et al. reported the total synthesis of (-)-(/ )-herbertenol via construction of the sterically-congested quaternary stereocenter by enantioselective C-C bond cleavage (Scheme 8.7) [26]. The symmetrical cyclobutanone 39 was prepared from 2-bromo-5-methylbenzaldehyde (38). Treatment of 39 with a catalytic amount of a rhodium(I)/SEGPHOS (5,5 -bis(diphenylphosphino)-4,4 -bi-l,3-benzodioxole) complex induced enantioselective cleavage of the prochiral C-C bond to produce indanone 40. Mechanistically, transmetalation of the boryl... 

A NHC-rhodium complex displayed an intriguing reactivity towards cyclobutanone derivatives. With complex 25, a cyclobutanone having an additional aldehyde function underwent chemoselective decarbonylation of the ketone moiety whilst the aldehyde carbonyl group remained intact, giving the corresponding cyclopropane in 82% yield (Scheme 8.7). On the other hand, no chemoselectivity was observed using [Rh(COD)Cl]2/dppp (dppp=l,3-bis(diphenylphosphino)propane), and both aldehyde and ketone units were decarbonylated to afford l-isopropenyl-4-propoxymethylbenzene in 84% yield. The use of the NHC ligand therefore provides a rare example of preferential activation of a C-C bond over a C-H bond. 

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