Of 1,5-enynes

Gold catalysts containing NHC ligands can also promote cycloisomerisation reactions. Bicyclo[3.1.0]hexanes 137-139 can be prepared from the cycloisomerisation of 1,5-enynes bearing a propargyUc acetate (135) in the presence of catalytic amounts of [AuCl(lPr)]/AgBF (Scheme 5.36) [41]. The cycloisomerisation reaction of 135 occurs by a 1,3-OAc shift/aUene-ene cyclisation/l,2-OAc shift sequence. Experimental results with allenyl acetate 136 support this hypothesis as 139 is obtained in higher ratios than 137 and 138 [41b],... 

Scheme 5.36 Golden catalysed cycloisomerisation of 1,5-enynes bearing a propargylic acetate...

Tab. 8.2 Rhodium-catalysed cycloisomerizaton of 1,5-enynes with phosphinite ligands ...

The use of 1,5-enynes instead of 1,6-enynes delivered bicycle derivatives such as 282 [157], and a hydroxy group in the tether enabled the formation of rings (284), as reported by Grise and Barriault (Equation 8.71) [158]. 

IJ-Enynes.1 (Propargyl)dicobalt hexacarbonyl cations (8, 148-149) couple with allylsilanes to give complexes of 1,5-enynes, generally in satisfactory yields. A typical reaction is formulated in equation (I). 

Negishi, E.-I. Rand, C. L. Jadhav, K. P. Highly selective and convenient method for the synthesis of 1,5-enynes and 1,5-dienes by the reaction of 1,3-dilifhiopropargyl phenyl sulfide with allylic halides. J. Org. Chem. 1981, 46, 5041-5044. 

The cyclization of 1,5-enynes to give bicyclo[3.1. Ojhexanes under mild conditions was reported by Toste (equation 44). Interestingly, in a similar reaction, Gagosz found that 1,5-enynes gave the expected bicyclo [3.1. OJhexane... 

Yet the first examples of cyclization of 1,5-enynes with gold were disclosed by the group of Arcadi in the context of a new synthesis of pyridines (equation 48). The cyclization of propargyl enamines catalyzed by sodium tetrachloroaurate gives substituted pyridines in a general way. The enamines were formed in situ from propargylamine and the corresponding ketone. 

The intramolecular amination of 1,5-enynes proceeds similarly to the intramolecular hydroxycyclizations of related substrates to give the products shown in equations (60) and (61). The intermolecular reaction of 1,6-enynes with a series of carbamates RO2CNH2 or anilines ArNH2 has also been reported. ... 

Phenyl propargyl sulfide " and selenide are rapidly deprotonated by 2 equiv. of base. The resulting dilithio derivatives react at their allylic rather than at their alkynic carbon centers (Scheme 34, entries c and d). Reduction of the sulfides allows the synthesis of 1,5-enynes (Scheme 34, entry b), whereas oxidation of the selenides leads to a-phenylseleno-a,P-unsaturated carbonyl compounds (Scheme 34, entry... 

Selective reduction of allyl sulfides implies that no scrambling of the carbon-carbon double bond occurs during the process. Effectively this has proved to be the case especially when lithium in ethylamine is used, and the method has allowed the regio- and stereo-selective synthesis of a large variety of 1,5-dienes including squalene (Scheme 25, entry a), mukapolide (Scheme 25, entry b), dendrolasin (Scheme 25, entry c), the basic nucleus of crassin acetate (Scheme 25, entry d) from 7,7-dialkylallyl sulfides and allyl halides, and also of 1,5-enynes " from propargyl sulfides and allyl halides (Scheme 34, entry b). 

Enynes and 1,4,5-trienes. The reagent undergoes 1,6-addition to dienoic esters to give mixtures of 1,5-enynes and 1,4,5-trienes. An excess of reagent substantially increases the yields. The allene/acetylene ratio is strikingly sensitive to substitution on the 6-carbon of the substrate. 

Cycloisomerization of 1,5-enynes with gold complexes containing highly electron-donating Ugands proceed via carbene-like intermediates to give a bicyclo-[3.1.0]hexenes (Scheme 127). ... 

Kozmin has reported the formation of polyqrclic ethers via the gold(I) or gold(III)-catalyzed tandem enyne cydization/alkoxylation of 1,5-enynes that contained a tethered hydroxy group [126]. As an example, treatment of homopropargyUc alcohol 86 with a catalytic 1 1 mixture of (PPhs) AuCl and AgC104 at 20 °C led to isolation of 6-oxabicyclo[3.2.1]octene 87 in 89% yield (Scheme 12.15). Conversion of 86 to 87 presumably occurs via attack of the pendant alkene on a goldhydroxy group at the disubstituted alkenyl carbon atom. Protodeauration then releases heterocycle 87 (Scheme 12.15). 

In 2011, the Echavarren group reported a study about the dependence of the outcome of the cycloisomerization of 1,5-enynes on the ligand (see Scheme 9.28). With gold catalysts based on the electron-donating IPr ligand, the formation of a bicyclo[3.1.0]hexene 26 as the exclusive product is observed. Less electron-rich... 

Scheme 16.67 Gold-catalysed hydrojq - and alkoxy-cyclisation of 1,5-enynes.

Gagosz reported the 5-endo hydroxy- and alkoi -cyclisation of 1,5-enynes to afford functionalised cyclopentenes. Complex XXIV (1 mol%) was used as catalyst, the reaction proceeded at room temperature and the final products were isolated in moderate to excellent yields. Primary and secondaiy alcohols, phenols and water were successfully used as nucleophiles and incorporated in the products (Scheme 16.67). ... 

There are many examples of preparing cyclopentane structures from enynes by gold-catalyzed carbocyclization reactions. Toste et al. have reported that Au(l)-phosphine complexes act as superior catalysts for isomerization of 1,5-enynes to bicyclo[3.1.0]hexenes [124]. For example, treatment of 1,5-enyne (86) with 1 mol% of PhsP-AuPFfi in dichloromethane at room temperature results in formation of cyclopropane-fused cyclopentene (87) in 99% yield (Scheme 18.30). 1,6-Enynes also undergo similar cycloisomerization to five-membered cyclic compounds under the influence of cationic gold(l) catalysts [125, 126], Hydroxylated enynes are versatile precursors for cyclopentenones by gold-catalyzed cycloisomerization... 

The gold-catalysed cyclization/oxidative 3+2-cycloadditions of 1,5-enynes (57) with nitrosobenzene produced substituted isoxazoles (59) with high stereocontrol. The nitrosobenzene also acts as an oxidizing agent in this reaction. Alkenylgold carbocations (58) are important intermediates in this reaction sequence (Scheme 16). ... 

Gold-catalyzed cyclization of 1,5-enynes allows the synthesis of a wide variety of synthetically useful products (Scheme 1.22) [24, 160]. The mechanism of 1,5-enynes resembles the one of 1,6-enynes, cyclizing through an endocycUc pathway. 

Scheme 1.22 General overview for the gold-catalyzed cyclization of 1,5-enynes...

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