Gold -catalyzed cycloisomerization

An interesting example of a gold-catalyzed cycloisomerization of P-aminoallene 168 to tetrahydropyridine 169 is depicted below <06OL4485>. Patil et al. report a similar gold-catalized hydroamination of allenes to produce 2-vinyl piperidine 170 in good yield <06TL4749>. 

Disubstituted furans 62 are obtained from a gold-catalyzed cycloisomerization/dimerization pathway involving terminal allenyl ketones and a,(3-unsaturated ketones <00AG(E)2285>. 

The Diels-Alder reaction outlined above is a typical example of the utilization of axially chiral allenes, accessible through 1,6-addition or other methods, to generate selectively new stereogenic centers. This transfer of chirality is also possible via in-termolecular Diels-Alder reactions of vinylallenes [57], aldol reactions of allenyl eno-lates [19f] and Ireland-Claisen rearrangements of silyl allenylketene acetals [58]. Furthermore, it has been utilized recently in the diastereoselective oxidation of titanium allenyl enolates (formed by deprotonation of /3-allenecarboxylates of type 65 and transmetalation with titanocene dichloride) with dimethyl dioxirane (DMDO) [25, 59] and in subsequent acid- or gold-catalyzed cycloisomerization reactions of a-hydroxyallenes into 2,5-dihydrofurans (cf. Chapter 15) [25, 59, 60],... 

Hashmi et al. have developed a short and high-yielding synthetic approach towards functionalized indoline derivatives 227 following a reaction sequence that consists of a three-component aza-MBH reaction from furfural catalyzed by La(OTf)3 in combination with 3-HDQ, a simple sulfonamide propargylation and a gold-catalyzed cycloisomerization (Scheme 1.86). ... 

General procedure for the gold-catalyzed cycloisomerization of 1,6-enynes to conjugated diene ... 

Six-membered dienes with an exocyclic double bond can also be obtained by gold-catalyzed cycloisomerization of 1,6-enynes. This transformation is stereospecific i.e., substrates with defined double-bond geometries afforded the products as single stereoisomers (Scheme 4-23). Low temperatures and electron-withdrawing... 

Representative procedure for the gold-catalyzed cycloisomerization of cyclohexadienyl-substituted alkynes. 2-Tosyloctahydro-3a,5-methanocyclopropa[4, 5 ]cyclopenta[r,2 1.3]-cyclopropa [l,2-c]pyrrole... 

The 1,5-enynes can be prepared by rhenium-catalyzed coupling of propargyl alcohols with allyl silanes. This step can be conveniently combined with the gold-catalyzed cycloisomerization. 

Representative procedure for the gold-catalyzed cycloisomerization of protected a-aminoallenes. 2-Benzyloxymethyl-5-isopropyl-3-methyl-l-(toluene-4-sulfonyl)-2,5-dihydro-lH-pyrrol ... 

Representative procedure for the gold-catalyzed cycloisomerization of P-hydroxyallenes. (2R)-2-Methyl-2-[(2R)-4-methyl-6-(2-methylpropenyl)-5,6-dihydro-2H-pyran-2-ylmethylJ-l, 4-dioxaspiro[4.5Jdecane ... 

Representative procedure for the enantioselective gold-catalyzed cycloisomerization of y-hydroxyallenes. 4,4-Diphenyl-2-vinyltetrahydrofuran ... 

Building on the earlier work of Hashmi [15], Liu has reported the gold-catalyzed cycloisomerization and oxidative cyclization of (Z)-enynols [16,17]. As an example of the former transformation, treatment of the tetraphenyl enynol 7 with a catalytic amount of AuCh in dichloromethane at room temperature led to isolation of... 

Krause has reported the gold-catalyzed intramolecular endo-hydroalkoxylation of (3-hydroxyallenes to form dihydropyrans [103]. For example, treatment of a 70 30 diastereomeric mixture of (3-hydroxyallene 61 with a catalytic 1 1 mixture of AuCl and pyridine in dichloromethane led to isolation of dihydropyran 62 in 84% yield as a 70 30 mixture of diastereomers (Eq. (12.32)). This transformation was also catalyzed effectively by a 1 1 mixture of (PPh3)AuCl and AgBp4 in toluene. (3-Hydroxyallenes that possessed substitution at the internal allenyl carbon atom also underwent gold-catalyzed cycloisomerization with selective transfer of chirality from the allenyl... 

Krause [222] showed that gold-catalyzed cycloisomerization of a-aminoallenes results in the synthesis of 3-pyrrolines via outer-sphere amine addition (Scheme 15.42). This early result pointed toward the application of gold-catalyzed... 

Another possibility would be the use of allylic esters, which after a gold-catalyzed cycloisomerization with the carbonyl oxygen atom as the nucleophile deliver activated allylic intermediates which at the same time contain a vinylgold substructure. After transfer of an allyl cation to palladium(O), an oxidative addition to palladium, the vinylgold intermediate could transfer the organic moiety to palladium(II). A final reductive elimination would close the catalytic cycle. At the same time, no halide that potentially could deactivate the cationic gold(I) catalyst would be present. Indeed, Blum et al. [30] presented such systems. But... 

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