Rhodium -promoted intramolecular

The use of rhodium(II) acetate in carbenoid chemistry has also been extended to promoting intramolecular C/H insertion reactions of ketocarbenoids 277,280,280 ,). From the a-diazo-P-ketoester 305, highly functionalized cyclopentane 306 could thus be constructed in acceptable yields by regiospecific insertion into an unactivated... 

Cyclization to a morpholinolactone (59) occurs in the hydrolysis reaction of the di-A-hydroxylethylated compound (60). Compound (59) is rapidly hydrolysed by water to (61) but in file presence of equimolar amounts of amines (RNH2) or ammo acid derivatives (62) forms.56 A novel reaction of cyclic 2-diazo-l,3-dicarbonyl compounds (63) with lactones (64) affords the products (65) in the presence of rhodium acetate, Rh2(OAc)4.57 Lewis acid-promoted intramolecular additions of allylsilanes to lilac tones gave substituted cyclopentanes.58 A proposed transition state guided efforts to improve the stereoselectivity of the reaction. The reaction of a series of /1-lactone derivatives, such as (66)-(68), has been studied and they have been ling cleaved the reaction outcome is both Lewis acid and structure dependent.59... 

It is worthy of note that this reaction is still the subject of solid and productive interest, as shown by the following recent examples. Chiu has exploited a rhodium carbene-promoted intramolecular formation of a carbonyl ylid - cycloaddition cascade as the key reaction in the synthesis of the nucleus of the cytotoxic diterpenoids pseudolaric acids A and B [54]. Although the diastereoselectivity was preferential for the undesired isomer 64, use of Hashimoto s chiral rhodium catalyst Rh2(SBPTV)4 reversed the selectivity in favor of 65 (64 65, 1 1.4) [55] (Scheme 29). 

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). 

Trost et al. reported the first asymmetric total synthesis of pseudolaric acid B by exploiting a rhodium-catalyzed intramolecular [5-1-2] cycloaddition reaction of a vinylcyclopropane with an alkyne (Scheme 8.2) [4]. The vinylcyclopropane having a tethered alkyne moiety 12 was synthesized from chiral precursors 9 and 11. Treatment of 12 with a cationic rhodium(1) catalyst promoted the [5-1-2] cycloaddition reaction to form a [5.3.0]bicyclic skeleton of 13 in a diastereoselective fashion. A few steps of functional group transformations provided the alkoxycarbonyl... 

Intermolecular Rhodium-Caialyzed [5+2] Cycloadditions In 1998, Wender et al. reported the first examples of intermolecular metal-catalyzed [5+2] cycloadditions of VCPs with alkynes [32]. While several catalysts have been proved to be efficient in promoting intramolecular [5+2] cycloadditions of VCPs and alkynes, the intermolecular [5+2] process has been Umited until recently to the use of [RhCl(CO)2]2 [33]. The initial study revealed that internal, terminal, electron-rich, and electron-poor alkynes all participated in the [5+2] cycloaddition with VCPs, giving... 

An initial step of orthometallation probably also occurs when aniline is allowed to react with ethylene in the presence of a rhodium(I) catalyst. 2-Methylquinoline (10 turnovers relative to the metal) and JV-ethylaniline (30 turnovers) are formed after 72 h in what are probably two independent reaction pathways (Scheme 144).216 It is interesting to note that the intramolecular cyclization step in the proposed216 mechanism (Scheme 144) has precedent in the palladium-promoted quinoline synthesis reported by Hegedus et al.16 (see Scheme 142), but the transformation 118->119 is unusual in the chemistry of organometallic insertion reactions.106... 

Intramolecular hydrosilylations of functionalized alkenes followed by hydrogen peroxide oxidation provide powerful methods for organic syntheses86-88. The reactions of allylic O-dimethylsilyl ethers 59 promoted by platinum catalysts, e.g. Karstedt s catalyst and Pt(PPh3)2(CH2=CH2), or rhodium catalysts, e.g. Rh(acac)(COD) and [RhCl(CH2=CH2)2]2> proceed via 5-endo cyclization to give oxasilacyclopentanes 60 with a couple of exceptions in which siloxatanes 61 are formed (Scheme ll)87,89. 

Table IV compares this result to the steady-state luminescence of related species. For example, the addition of the doubly modified duplex to the ruthenium-modified duplex does not quench the luminescence from the ruthenium-modified duplex. The lack of luminescence demonstrates the absence of any adventitious quenchers in the rhodium(III) sample. Addition of an equimolar amount of rhodium-modified duplex to ruthenium-modified duplex also does not promote significant quenching of the ruthenium duplex, consistent with the quenching being substantially intramolecular at these concentrations. These studies complement the photocleavage experiments (Figure 6), from which we estimate less than 15% intermolecular interaction at these concentrations.

Intermolecular [3+2] 1,3-dipolar cycloaddition of a D-glyceraldehyde-derived nitrile oxide to the 4,5-double bond of 2-methylfuran gave a 60 40 diastereomeric ratio of the two furoisozaxoline isomers. This chemistry was employed in the synthesis of L-furanomycin <2005EJ03450>. As depicted in Scheme 43, an intramolecular cycloaddition of a furan with a carbonyl ylide dipole proceeded under rhodium-catalyzed microwave-promoted conditions to provide the cycloadduct in a modest yield <20040L3241>. 

The second approach involves several examples of intramolecular reactions which employ cyclopropenes with a diazoketone substituent. In these cases, copper and rhodium catalysts effectively promote the formation of bridged bicyclo[1.1.0]butanes. ... 

A rhodium(III) catalyst was also shown by Witulski and Schweikert to promote the intramolecular oxidative cyclization of bisindolylmaleimides to indolocarbazoles as a key step in the synthesis of cytotoxic agents of the... 

Conjugate addition reaction is also promoted by superbases. Novikov et al. reported that the intramolecular Michael addition of a,p-unsaturated ester 31, which was obtained from vinyl diazoacetate in the presence of rhodium acetate [Rh2(OAc)4], proceeded with DBU to give the spirocyclic indole skeleton 32 in 90% yield [7] (Scheme 7.5). This strucmre can be seen in intriguing, complex natural products, such as marcfortines 33 and 34. 

The ability of rhodium or copper complexes to promote carbene formation allows the study of asymmetric reactions with chiral ligands attached to the metal centre. Some highly enantioselective transformations are possible in certain cases. For example, the lactone 101 was formed with high optical purity using the complex [Rh2(5S-MEPY)4] (4.79). In the absence of competing intramolecular reactions, intermolecular C—H insertion is possible and such reactions are also amenable to asymmetric induction. Thus, high enantioselectivity in the insertion into a C—H bond of cyclohexane has been reported (4.80). 

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