Domino reactions alkene insertion

A interesting and useful reaetion is the intramolecular polycyclization reaction of polyalkenes by tandem or domino insertions of alkenes to give polycyclic compounds[l 38]. In the tandem cyclization. an intermediate in many cases is a neopentylpalladium formed by the insertion of 1,1-disubstituted alkenes, which has no possibility of /3-elimination. The key step in the total synthesis of scopadulcic acid is the Pd-catalyzed construction of the tricyclic system 202 containing the bicyclo[3.2. Ijoctane substructure. The single tricyclic product 202 was obtained in 82% yield from 201 [20,164). The benzyl chloride 203 undergoes oxidative addition and alkene insertion. Formation of the spiro compound 204 by the intramolecular double insertion of alkenes is an exam-ple[165]. 

Intramolecular version can be extended to polycyclization as a one-pot reaction. In the so-called Pd-catalysed domino carbopalladation of trienediyne 178, the first step is the oxidative addition to alkenyl iodide. Then the intramolecular alkyne insertion generates 179. One alkyne and two alkene insertions are followed. The last step is the elimination of /f-hydrogen. In this way, the steroid skeleton 180 is constructed from the linear trienediyne 178 [78]. 

Several other types of domino reactions have been employed in the synthesis of natural products. Diastereoselective conversion of allylic carbonate 173 into enone 174 was one key transformation in a total synthesis of (+)-3-isorauniticine 175 (Scheme 27).Treatment of allylic sulfonamide 173 with a palladium catalyst re-gioselectively forms a 7r-allylpalladium intermediate by carbonate displacement. Carbopalladation of the pendant alkene, carbonylation, a second intramolecular alkene insertion, and /3-hydride elimination delivers a 67 22 11 mixture of stereoisomers of which enone 174 is the major product (isolated in 45-53% yield). Carbopalladation products can also undergo anion capture reactions. For instance, during the synthesis... 

The palladium(II)-catalyzed olefin carbonylation reaction was first reported more than 30 years ago in studies by Stille and co-workers and James et al. The reaction of carbon monoxide with cis- and tra 5-but-2-ene in methanol in the presence of palladium(II)-chloride and copper(II)-chloride yielded threo- and eryt/zro-3-methoxy-2-methyl-butanoate, respectively. The transformation that was based on the well-known Wacker process for oxidation of ethylene into acetaldehyde in water " is now broadly defined as the Pd(II)-catalyzed oxycarbonylation of the unsaturated carbon-carbon bonds. This domino reaction includes oxypalladation of alkenes, migratory insertion of carbon monoxide, and alkoxylation. Since the development of this process, several transformations mediated by palladium(II) compounds have been described. The direct oxidative bisfunctionalization of alkenes represents a powerful transformation in the field of chemical synthesis. Palladium(II)-promoted carbonylation of alkenes in the presence of water/alcohol may lead to alkyl carboxylic acids (hydrocarboxylation), diesters [bis(aIkoxycarbonyla-tion)], (3-alkoxy carboxylic acids (alkoxy-carboxylation), or (3-alkoxy esters (alkoxy-carbonylation or alkoxy-alkoxy-carbonylation). Particularly attractive features of these multitransformation processes include the following ... 

The domino carbonylation and Diels-Alder reaction proceed only as an intramolecular version. Attempted carbonylation and intermolecular Diels-Alder reaction of conjugated 2-yne-4-enyl carbonates 101 in the presence of various alkenes as dienophiles give entirely different carbocyclization products without undergoing the intermolecular Diels-Alder reaction. The 5-alkylidene-2-cyclopenten-4-onecarboxy-lates 102 were obtained unexpectedly by the incorporation of two molecules of CO in 82% yield from 101 at 50 °C under 1 atm [25], The use of bidentate ligands such as DPPP or DPPE is important. The following mechanism of the carbocyclization of 103 has been proposed. The formation of palladacyclopentene 105 from 104 (oxidative cyclization) is proposed as an intermediate of 108. Then CO insertion to the palladacycle 105 generates acylpalladium 106. Subsequent reductive elimination affords the cyclopentenone 107, which isomerizes to the cyclopentenone 108 as the final product. 

The decomposition of 368 catalysed by Rh perfluorobutyrate and subsequent intramolecular cycloaddition give 370 in high yield (93%) as the key step in the total synthesis of lysergic acid (371), and is believed to involve the intramolecular reaction of the ylide intermediate 369 at the alkene. No C—H insertion takes place [122], Another elegant example is the efficient construction of the aspidosperma alkaloid skeleton 374. The Rh-catalysed domino cyclization cycloaddition of diazo irnide 372 afforded cycloadduct 374 in 95% yield as a single diastereomer via the dipole 373, and desacetoxy-4-oxo-6,7-dihydrovindorosine (375) has been synthesized from 374 [123]. 

There are several possible reaction paths in the carbonylation of l-iodo-1,4-, 1,5-, and 1,6-dienes, and chemoselectivity depends on reaction conditions and ligands. For example, the 1-iodo-1,4-diene 78 reacted with two CO molecules to give the keto ester 79 in high yield by domino insertion of CO, alkene, and CO [36]. The diketo ester 81 was obtained from iodotriene 80. In this reaction, domino insertion of CO, alkene, and CO occurred to give rise to the diketo ester 81 in 54 % yield. The bicyclic monoketo ester 82 was formed in 14 % yield by premature tr ping of acylpalladium intermediate with MeOH [37]. 

D. DOMINO AND CASCADE REACTIONS INITIATED BY 17-allylpalladium insertion into alkenes or ALKYNES... 

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