Ring-closing enyne

Enyne Cross Metathesis and Ring-Closing Enyne Metathesis.348... 

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

More research efforts have focused on the ring-closing enyne metathesis, which usually [176] provides conjugated vinyl cycloalkenes (cf Fig. 2a, exo mode) useful for further manipulation, but also allows tandem metathesis processes for the formation of polycyclic compounds. 

Clark s group also reported on ring-closing enyne metathesis for the preparation of six- and seven-membered cyclic enol ethers 428 n= 1,2) as potential building blocks for the synthesis of marine polyether natural compounds such as brevetoxins and ciguatoxins. Metathesis products 428 were obtained from ene-ynes 427 in 72-98% yield when the NHC-bearing catalyst C was used (Scheme 84) [179]. 

For leading references, and the application of this method to ring-closing enyne metathesis, see Storm Poulsen C, Madsen R (2002) J Org Chem 67 4441... 

Bicyclic dienic products recently synthesized by this method (Scheme 36) are lactams 144a and b (07T8267) and enamine ester 145 (09CEJ4565). The precursor of the latter substance originates from a four-component synthesis followed by y-allylation. The alternative y-propargylation and subsequent ring-closing enyne metathesis performed under an ethene atmosphere lead to the 8-vinyl derivative of product 145. 

A highly functionalized conjugated diene has been synthesized through sequential silicon-tethered ring-closing enyne metathesis by ruthenium-carbene catalyst Ic followed by Tamao oxidation (Equation (9)). ... 

A versatile route for the synthesis of a phosphorus oxide template is presented (Scheme 12). Ring-closing enyne metathesis using Ig on these types of substrates 37a and 37b led to the formation of mono- and bicyclic phosphorus heterocycles 38a and 38b. 

The ring-closing enyne metathesis has been used for the synthesis of alkenyl substituted six- and seven-membered cyclic enol ethers (Eq. 88) [144]. The reaction has been proposed as an element of the strategy for preparation of subunits of brevetoxins and ciguatoxins. 

An efficient method for the preparation of highly functionalized conjugated dienes with the use of silicon-tethered ring-closing enyne metathesis in the presence of first- and second-generation Grubbs catalysts has been described... 

A catalytic tandem cyclopropanation-ring-closing metathesis of dienyne 80 led to derivative 81 in good yield (Scheme 30 <2004JA9524>). For internal alkynes, carbene-mediated ring-closing enyne metathesis was observed. Less favorable alkyne binding leads to preferential reactions of the metal carbene with the 1-alkene moiety. 

Mono- and bicyclic phosphorus heterocycles 199, 200, 202, and 203 were synthesized starting from the bifunctional phosphorylating agent bis(diisopropylamino)ethynyl phosphine 195 via ring-closing enyne metathesis using 4,5-dihydroimidazol-2-ylidene ruthenium benzylidene complex, as a catalyst. Bicyclic phosphorus oxides 199 were obtained in 66-83% yield, whereas phosphorus borane derivative 202 was isolated in 74% yield <2001TL8231>. 

A. Fiirsmer and L.Turet, Concise and practical synthesis of latrunculin A by ring-closing Enyne-Yne metathesis, Angew. Chem. Int. Ed., 2005,44(22), 3462. 

Kitamura, T., Mori, M. Ruthenium-catalyzed ring-opening and ring-closing enyne metathesis. Org. Lett. 2001, 3, 1161-1163. 

Scheme 44. Ring-closing enyne metathesis using Grabbs catalyst for the synthesis of ( )-stemoamide.

Scheme 45. Ring-closing enyne metathesis to form 10-12-membered macrocycles.

Scheme 74. Tandem ring-closing enyne metathesis using first generation Grubbs catalyst to form...

Ring closing enyne metathesis as a powerful tool for the synthesis of heterocydes 07CSR55. 

Ring-closing enyne metathesis was also attempted by the group of Perez-Castells for the synthesis of vinylindoles (04JOC2084). However, they obtained a mixture of desired vinylindole, as well as dimerized product (not shown). Depending on the reaction times and dilution, the major product of the reaction could be altered. Mori and co workers performed a tandem enyne metathesis/Diels—Alder/oxidation approach for the synthesis of indoles (06T3872). However, both indoles along with indolines were obtained in low yields. 

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