Enol triflates cross-coupling

The key step in a short and efficient synthesis of pleraplysillin-1 (127) is the palladium-catalyzed cross-coupling of vinylstannane 125 with vinyl triflate 126 (see Scheme 33). This synthesis is noteworthy in two respects. First, vinyl triflate 126 is generated regio-specifically from the kinetic enolate arising from a conjugate reduction of enone 124 the conjugate reduction of an enone is, in fact, a... 

Stannyl derivatives of 2ff-pyran-2-one, accessible from bromopyranones by cross coupling with organotin reagents, themselves take part in Pd(0)-catalyscd cross coupling with enol triflates. This methodology offers a new approach to steroidal pyran-2-ones <96JOC6693>. 

An application of Stille couplings to the solid phase using a traceless A-glycerol linker with 2-stannylindoles has been developed [177]. Only a few examples of the use of 3-stannylindoles in Stille reactions have been described. Ortar and co-workers prepared 169 and 170 and effected Pd-catalyzed cross coupling reactions with several aryl, heteroaryl, and vinyl substrates (bromides, iodides, triflates) to give the expected products 171 in high yields [178]. Enol triflates behave exceptionally well under the Ortar conditions, e.g., 172 to 173. 

Clavepictines A and B were prepared using a variety of effective reactions on the piperidine ring, such as a silver-promoted cyclization of an aminoallene intermediate, diastereoselective alkylation, and cross coupling of an enol triflate <99JA10012>. 

The insight that zinc ester enolates can be prepared prior to the addition of the electrophile has largely expanded the scope of the Reformatsky reaction.1-3 Substrates such as azomethines that quaternize in the presence of a-halo-esters do react without incident under these two-step conditions.23 The same holds true for acyl halides which readily decompose on exposure to zinc dust, but react properly with preformed zinc ester enolates in the presence of catalytic amounts of Pd(0) complexes.24 Alkylations of Reformatsky reagents are usually difficult to achieve and proceed only with the most reactive agents such as methyl iodide or benzyl halides.25 However, zinc ester enolates can be cross-coupled with aryl- and alkenyl halides or -triflates, respectively, in the presence of transition metal catalysts in a Negishi-type reaction.26 Table 14.2 compiles a few selected examples of Reformatsky reactions with electrophiles other than aldehydes or ketones.27... 

McMurry enol triflate/cuprate cross coupling... 

The McMurry-Scott cross coupling reaction22 between enol triflates and organocuprates generally proceeds with retention of the configuration in the parent enol triflate component. In these reactions it is widely assumed that a planar alkenylcopper(III) intermediate is formed by oxidative... 

The enol triflates derived from tetrahydropyran-2-ones undergo a cross-coupling with benzenethiols catalysed by Ni(0) that gives the 6-arylsulfanyl-3,4-dihydro-2//-pyrans, readily oxidised to the stable sulfoxides. The latter undergo facile conversion to the a-lithiated enol ethers <03S584>. 

The cross-coupling of organozinc compounds has been accomplished using a number of metal enolate complexes, namely Rh(acac)(H2C=CH2)2 (6) , Co(acac)3 (30) °, Ni(acac)2 (47) , Li(acac) (107) and Cr(acac)3 (108) . For instance, complex 47 proved to be an extremely effective catalyst system for the Negishi cross-coupling of arylzinc halides (109) with aryl (110), heteroaryl and alkenyl halides, triflates and nonaflates to give the corresponding biaryl compounds (111) (equation 30). The solvent played an important role in these reactions and optimal conditions were found with 8 1 mixtures of THF and A-ethylpyrrolidinone (nep). Only 0.05 mol% of the nickel complex... 

Intramolecular Cross-coupling of Enol Triflates with Organoboron... 

Intramolecular cross-coupling of enol triflates with organoboron... 

These ease of preparation of vinyl and aryl triflates and the availability of the starting materials have expanded their use as a coupling partner with a terminal acetylene. Facile Pd-Cu coupling of vinyl triflates with terminal acetylenes was reported by Cacchi [51]. The cross-coupling of enol triflate 88 with phenylacetylene proceeds easily under normal conditions [Eq. (33)] [52]. For the double cross-coupling of aromatic 1,2-ditriflates with TMSA, the addition of Bu4NI accelerates enediyne formation [Eq. (34)] [53]. 

Another approach developed by the Vogel group relies on a carbonylative Stille cross-coupling between stannylated glucal derivative 410 and enol triflate 412 derived from isolevoglucosenone [152] (O Scheme 80). 

Hong, F.-T., Paquette, L. A. Olefin metathesis in cyclic ether formation. Direct conversion of olefinic esters to cyclic enol ethers with Tebbe-type reagents. Copper(l)-promoted Stille cross-coupling of stannyl enol ethers with enol triflates construction of complex polyether frameworks. Chemtracts t997, 10,14-19. 

A new route to conjugated enynes has been reported which involves cross-coupling of enol triflates with 1-alkynes in the... 

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