Rhodium-catalysed heterocycle

Rhodium-catalysed asymmetric cyclization/hydroboration followed either by Pd-catalysed arylation or by oxidation was applied to the synthesis of a number of chiral, non-racemic carbocycles and heterocycles. Thus, reaction of enyne (28) with catecholborane, catalysed by a 1 1 mixture of [Rh(COD)2]+ Sbly,- and (S)-BINAP (5 mol%), followed by Pd-catalysed arylation with /7-IC6H4CF3, afforded benzyli-denecyclopentane (29) in 65% yield with 88% ee.46... 

Iodonium ylides (136), generated in situ with bisacetoxyiodobenzene, are converted to allyl- or benzyl-substituted oxonium or sulfonium ylides (137) via rhodium- or copper-catalysed carbene transfer.115 Such ylides undergo [1,2]- or [2,3]-rearrangement to the corresponding 2-substituted heterocycles (138). An example of the rhodium-catalysed reaction is reported in Scheme 36. 

The rhodium A-heterocyclic carbine complex [Rh(IMes)(COD)] [IMes = A,A -bis(2,4,6-trimethylphenyl)imidazol-2-ylidine COD = cycloocta-1,5-diene] catalyses the 4 + 2 + 2-carbocyclization of 1,6-enynes (191) to carbocycles [(192) and (193)] (Scheme 54).226 Computational and experimental evidence of a new reaction pathway for the diastereospecific intermolecular rhodium-catalysed 4 + 2 + 2-carbocyclization (g) reactions of 1,6-enynes with r-components has been reported.227... 

Rische T, Muller K, Eilbracht P (1999) One-pot synthesis of pharmacologically active diamines via rhodium-catalysed carbonylative hydroaminomethylation of heterocyclic allylic amines. Tetrahedron 55 9801-9816... 

Rapoport and co-workers have reported a general synthesis of nitrogen, oxygen, and sulphur heterocycles (218) by rhodium-catalysed intramolecular N-H, 0-H, or S-H insertion reactions.of keto-ester precursors (217)- This reaction is well documented as an efficient route to B-lactams but this group has now shown that the reaction works well for the synthesis of five-and six-membered nitrogen heterocycles (Scheme 22). The reaction fails for seven-membered nitrogen heterocycles in this case C-H insertion to give a eyelopentanone is the preferred reaction mode. 

A synthesis of 4//-quinolizines from 2-vinylpyridine and alkynes catalysed by rhodium-Af-heterocyclic carbenes has been reported (Scheme 157). ... 

Dinitrogen-fused heterocycles have been formed in high yield by thermal 3-1-2-cycloadditions of two types of azomethine imines with allenoates. Rhodium-catalysed formal 3 -l- 2-cycloadditions of racemic butadiene monoxide with imines in the presence of a chiral sulfur-alkene hybrid ligand have furnished spirooxindole oxazolidines and 1,3-oxazolidines stereoselectively. ° Formation of 1,2-disubstimted benzimidazoles on reaction of o-phenylenediamine with aldehydes is promoted by fluorous alcohols that enable initial bisimine formation through electrophilic activation of the aldehyde. 

Seven-membered aza-heterocycles have been prepared from a rhodium-catalysed tandem 2,3-rearrangement/heterocyclization (Scheme 44). ... 

A 2-aminodiaryl ether (79.2, X = O) is cyclized to the furopyridine (79.3, X = O) by using the Pschorr reaction—thermolysis ofa mixture of the diazonium salt and copper powder. The use of heterocyclic diazonium salts in organic synthesis has been reviewed [2980]. Rhodium(II) acetate catalyses the room-temperature cyclization of a-diazo-jS-oxo esters (79.4) by carbenoid insertion into a benzenoid C—H bond. 

Rhodium(I)-catalysed 2 + 2 + 2-cycloadditions of ene-allene (96) with allene (97) yielded trans-fused hydrindanes (98) and decalins with high regio- and stereo-selectivities (Scheme 31). A Ni-phosphine complex catalysed the 2 + 2 + 2- (g) cycloaddition of diynes with substituted ketenes to produce 2,4-cyclohexadienones in high yields. No decarbonylation products were observed. The chiral A-heterocyclic carbene-catalysed enantioselective 2 + 2 + 2-cycloaddition of ketenes with CS2 produced l,3-oxatian-6-ones in good yields and with high enantioselectivities. 2" ... 

The Miyaura and Batey groups have also independently reported the use of rhodium catalysts for addition to aldehydes in the presence of phosphine ligands.Tautens has shown that [Rh(cod)Cl]2-catalysed reactions of heterocyclic alkynes with arylboronic acids in the presence of water-soluble ligands and sodium dodecyl sulfate (SDS) and sodium carbonate as bases affords trisubstituted alkenes in high regio-selectivity. ... 

While these reactions allowed ready access to oxygen heterocycles having the adjacent hydroxy and vinyl groups in a cis-disposition, access to the corresponding trans-derivatives was more difficult due to a lack of generally applicable routes (16, 17) to E-y-alkoxy allylboronates. We therefore eventually developed a new route to this entity based on a rhodium or zirconium catalysed hydroboration of ynol ethers. (18)... 

The above in situ strategy was also applied to Schiff base substrates (in Ueu of aldehydes or ketones), affording azuidination products in fair yield, moderate dr, and outstanding enantioselectivity [44, 45]. The specific examples of benzyUdene transfer illustrated in Table 4 confirm that electron-poor (entry 1), electron-rich (entry 4), aliphatic (entry 2), and a,p-unsaturated groups are tolerated in the A-SES imine electrophiles. As shown in Scheme 17, the utility of the method was showcased in an unconventional preparation of paclitaxel side-chain 49 that ultimately begins with 3-furfural. The optically pure heterocyclic aziridine 48 was obtained as an inconsequential diastereomeric mixture by the trio of coordinated phase transfer, achiral rhodium, and chiral sulfide catalyses, albeit in the antipodal series (see ent-47) subsequent conversicm to the target amido ester was by way of standard manipulations [130]. 

---