A, -Enynes

Fig. 2a-c Typical enyne metathesis reactions ring-closing enyne metathesis (a) enyne cross metathesis (b and c)... 

One of the subunits of the natural product (-)-macrolactin A, a strong anti-viral agent, has been synthesized as shown in the following scheme, involving the hydrotelluration of a enyne (a), and the opening of an epoxide with a vinylic higher-order cyanocuprate (b). ... 

Scheme 43. (a) Enyne metathesis using first generation Grubbs Ru-caibene catalyst. 

Scheme 51. (a) Enyne metathesis to form five-membered products using Pd(0). (b) Mechanism illustrating the formation of an unusual alkenylpalladium intermediate via a n-allylpalladium species. 

It was obvious that 37 and the enyne generated a enyne metathesis catalytic species. Stoichiometric reactions in the presence of B(Ar )4 anion revealed by NMR the production of acrolein and the new alkenylcarbene 39, assumed to be generated by retroene reaction from the intermediate 38 (Scheme 26). 

A reaction involving cychzation of an a-enynic alcohol and rearrangement to a furane was carried out as early as 1946 (Heilbron et al., 1946). 

The precursor relationship of an a-enynic alcohol to carhna oxide (II) receives some support from the isolation of the alcohol (LVIII) from carhna species (Sorensen, i960). [See also addendum ]. 

This route involves internal addition in a /8-enynic alcohol and is reminiscent of the proposed biogenetic scheme for furanes (see above) involving internal addition in an a-enynic alcohol. 

This isomerization, which must proceed through a 1,2,3-trienylanine, is not "contra-thermodynamic", since with a catalytic amount of potassium tert.-butoxide the same result is obtained. Enyne ethers, H2C=CH-CsC-0R, undergo a similar conversion into HCeC-CH=CH-OR upon interaction with alkali metal amides in liquid NH3, followed by hydrolysis . Enyne sulphides, H2C=CH-CsC-SR, and the hydrocarbons H2C=CH-CsC-R (R = or phenyl) give only tars or polymeric products under... 

A mixture of 1 g of KO-terfc.0.6 g of HO-tert.-CgHg and 40 ml of dry, pure HHPT was warmed at 40-50°C until all of the solid material had disappeared. The solution obtained was cooled to 15°C and 15 g of the enyne ether (note 1) were added in 2 min. The temperature of the mixture was kept at aa. 25°C and after the addition this temperature was maintained for an additional 10 min. 

As indicated in the general scheme below, butatrienes are the first products from base-induced 1,4-elinination of hydrogen and a suitable leaving group. The butatriene in general very readily undergoes isomerization into enynes, if sufficiently "acidic" protons are available (see Chapter 11 in Ref. 3a). In aprotic media cumulenic ethers are fixed as their lithio derivatives if an excess of alkyllithium is applied... 

Treatment of conjugated enyne systems, H C-C=C-CeC-CH-OR, with a suitable base in principle may give rise to 1,6-elimination of HOR with primary formation of the system C=C-C=C=C=C, which subsequently may undergo isomerization to a dienyne. ... 

Vote 2. A large excess of R MgCl is required, as the subsequent metallation of the enyne is rapid. In the case of C2H5 the Grignard reagent was prepared from ethyl bromide. 

To a solution of 0.10 mol of the enyne alcohol (see Chapter III, Exp. 41) in 140 ml of dry diethyl ether was added in 15 min with cooling at about -30°C a solution of 0.22 mol of ethyllithium in about 180 ml of diethyl ether (see Chapter II, Exp. 1). The clear solution was then warmed to 25 C and after standing for 10 min at that temperature, it was cautiously poured into 200 ml of an aqueous solution of 30 g of NH,C1. The layers formed after standing were separated, and the aqueous layer was extracted three times with diethyl ether. The combined... 

The benzene derivative 401 by the intermolecular insertion of acrylate[278], A formal [2 + 2+2] cycloaddition takes place by the reaction of 2-iodonitroben-zene with the 1,6-enyne 402. The neopentylpalladium intermediate 403 undergoes 6-endo-lrig cyclization on to the aromatic ring to give 404[279],... 

In the coupling of the allenyl ester 7 with a terminal alkyne, an electron-deficient phosphine (Ph3P) gave the enyne-conjugated ester 8 as the major product, while an electron-rich phosphine (TDMPP or TTMPP) yielded the non-conjugated enyne esters ( )- and (Z)-9[4],... 

Depending on the substituents of l,6-enynes, their cyclization leads to 1.2-dialkylidene derivatives (or a 1.3-diene system). For example, cyclization of the 1,6-enyne 50 affords the 1.3-diene system 51[33-35]. Furthermore, the 1.6-enyne 53, which has a terminal alkene, undergoes cyclization with a shift of vinylic hydrogen to generate the 1,3-diene system 54. The carbapenem skeleton 56 has been synthesized based on the cyclization of the functionalized 1,6-enyne 55[36], Similarly, the cyclization of the 1,7-enyne 57 gives a si -mem-bered ring 58 with the 1,3-diene system. 

Another interesting transformation is the intramolecular metathesis reaction of 1,6-enynes. Depending on the substrates and catalytic species, very different products are formed by the intramolecular enyne metathesis reaction of l,6-enynes[41]. The cyclic 1,3-diene 71 is formed from a linear 1,6-enyne. The bridged tricyclic compound 73 with a bridgehead alkene can be prepared by the enyne metathesis of the cyclic enyne 72. The first step of... 

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