Dienyl triflate

Allylic amines are coupled to halides giving either allylic amines or enamines depending on the reaction condition. Reaction of steroidal dienyl triflate with Boc-diprotected allylamine affords allylamine. Use of AcOK as a base is crucial for the clean coupling[102]. The tert-allylic amine 123 reacts with an aryl halide to give the enamine 125 in DMF and allylic amine 124 in nonpolar solvents[103]. 

In presence of NaUMDS the enolate of enone 9 is formed at -78 °C. Reaction of the enolate with Comins reagent (2-[7V,7V-bis(trifluoro-methylsulfonyl)amino]-5-chloropyridine) provides dienyl triflate 10. 

The introduction of the aminoethyl side chain is accomplished by Suzuki cross-coupling of dienyl triflate 10 with the alkyl borane generated by hydroboration of A -vinyl- er butyl carbamate (11) with 9-BBN. ... 

Dienyl triflates can also be used in such couplings to give the 122... 

Reaction with Dicarbonyl Compounds. 1,3-Diketones can be reacted with an equimolar amount of Tf20 or in excess to furnish the corresponding vinyl triflates or dienyl triflates (eq 22). These triflates are transferred into monoketones, monoalcohols, alkanes, and unsaturated ketones by means of various reducing reagents. ... 

Reaction of dimethyl phosphonate (74) with the steroidal dienyl triflate 73 gave the dimethyl alkenylphosphonate 75 [23]. Dimethyl alkynylphosphonate (77) was produced in one step by the reaction of 1,1-dibromo-l-alkenes 76 with dimethyl phosphonate (74) in DMF using Pd(OAc)2-DPPF as a catalyst and propylene oxide as a scavenger of HBr. The expected monocoupling product, bromovinylphos-phonate, was not obtained [24]. Phosphonates 78 can be converted to arylphos-phines 79 by reaction with aryl Grignard reagents, followed by reduction with HSiCls [25]. 

An alternative route using dienyl triflate ligands with a zinc-mediated cobaloxime reduction has also been used for simple cobaloxime-substituted alkenes 177 (Equation (24)). ... 

These Mo catalysts with a C2-tether connecting the phosphine and cyclopenta-dienyl ligand provide an example of the use of mechanistic principles in the rational design of improved catalysts, in this case based on information about a decomposition pathway for the prior generation of catalysts. The new catalysts offer improved lifetimes, higher thermal stability, and low catalyst loading. The successful use of a triflate counterion and solvent-free conditions for the hydrogenation are additional features that move these catalysts closer to practical utility. 

With (i ,i )-BINAP as the ligand, Keay and Lau have been able to achieve the cascade cyclizations of the dienyl-substituted aryl triflates 134 toward the total synthesis of the natural product (+)-halenaquinone with ee s of up to 96% (Scheme 35). For these substrates, they observed an interesting influence of the remote substituent in 134. ... 

The procedure is also applicable to dienyl iodides, as well as bromides and triflates to afford cyclopentenones in high yields (Equation (32)). ... 

The key step of this synthesis is a sequential asymmetric Heck-N-acyliminium ion cyclization of dienyl carbamate triflate 13 to provide enantiopure 3,4-dihydro-9a,4a-(iminoethano)-9/f-carbazole 16. This intermediate and related structures containing a 2,3-double bond should represent versatile precursors for constructing a variety of pentacyclic indole alkaloids containing the (hydroiminoethano)-carba-zole fragment. 

Vinyl triflates can be coupled efficiently to various organotin compounds. Further details of this chemistry have now appeared including efficient preparations of trimethylsilyldienes (Scheme 33).71 Two other routes to silyldienes are outlined in Scheme 34. Reduction of allenic alcohols (21) gave moderate yields of the dienyl products, although the stereoselectivity of the process leaves much to be desired. The second method, involving hydroboration of the allene (22) is much more stereoselective and enables either isomer of the final product to be obtained depending on the elimination conditions used. A key application for such dienes is in Diels-Alder reactions, where the products have vinylsilane functionality for further modification. This type of chemistry has now been explored with 2,3-bis(trimethylsilyl)buta-1,... 

Stereoselective syntheses of the trienes 71 and 73 were carried out in very high yields by the coupling of the dienyl nonaflate 69 with the (E)- and (Z)-alkenylstannanes 70 and 72 in the presence of AsPhs as a ligand in DMF at room temperature. The nonaflate was found to be more reactive than the corresponding triflate [34]. 

In another beautiful application, Overman et al. developed the total synthesis of the natural product (+)-minfiensine (130), having a l,2,3,4,-tetrahydro-9a,4a-(iminoethano)9H-carbazol core (Scheme 7.29) [80]. The key step in their synthesis is a tandem process consisting of a catalytic asymmetric Mizoroki-Heck ring closure and an N-acyliminium ion cyclization of dienyl carbamate triflate 127 (127—>128). The reaction proceeded smoothly using the Pfaltz ligand (S)- Bu-PHOX (85), providing (dihydroiminoethano)carbazole 129 after the addition of excess trifluoroacetic acid, with 75% overall yield and 99% enantiomeric purity (127 129). 

In the case of oxygen leaving groups, not only aryl and vinyl triflates [36], but also dienyl phosphates [108] and aryl sulfamates such as 175 [109] can be used efficiently (Scheme 5.38). 

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