Triflates hydrogenation

The aryl- and heteroarylfluorosilanes 541 can be used for the preparation of the unsymmetrical ketones 542[400], Carbonylation of aryl triflate with the siloxycyclopropane 543 affords the 7-keto ester 545. In this reaction, transme-tallation of the siloxycyclopropane 543 with acylpalladium and ring opening generate Pd homoenolate as an intermediate 544 without undergoing elimination of/3-hydrogen[401],... 

TMS triflate [27607-77-8] is an extremely powerful sdylating agent for most active hydrogens. It surpasses the sdylating potential of TMCS by a factor of nearly 10. It readily converts 1,2- and 1,3-diketones into disilylated dienes (7). 

Treatment of 8-azidomethylperhydropyrido[l,2-c]pyrimidin-l-one 157 with methyl triflate and catalytic hydrogenation of the azide group led to the formation of tricyclic guanidine derivative 158 (01JA8851). Hydroxy group of 149 was protected with methoxymethyl chloride, and the p-methoxybenzyl protecting group (PMB) was eliminated by treatment with DDQ. 

Some exceptions to this general observation were found halide and nitrite salts have unusually high hydrogen-bond basicities (as would be expected), while penta-cyanopropionide, picrate, triflate, and perfluorobezenesulfonate salts not only had unusually low hydrogen-bond basicities (also as would be expected) but also lower s values, perhaps due to the weakening of the Coulombic interactions by delocalization of the charge on the anions. 

A synthetically useful virtue of enol triflates is that they are amenable to palladium-catalyzed carbon-carbon bond-forming reactions under mild conditions. When a solution of enol triflate 21 and tetrakis(triphenylphosphine)palladium(o) in benzene is treated with a mixture of terminal alkyne 17, n-propylamine, and cuprous iodide,17 intermediate 22 is formed in 76-84% yield. Although a partial hydrogenation of the alkyne in 22 could conceivably secure the formation of the cis C1-C2 olefin, a chemoselective hydrobora-tion/protonation sequence was found to be a much more reliable and suitable alternative. Thus, sequential hydroboration of the alkyne 22 with dicyclohexylborane, protonolysis, oxidative workup, and hydrolysis of the oxabicyclo[2.2.2]octyl ester protecting group gives dienic carboxylic acid 15 in a yield of 86% from 22. 

A solution of 1 equivalent of the oxazolidinone in diethyl ether is cooled to —78 C. To the resultant suspension are added 1.4 equivalents of triethylamine. followed by 1.1 equivalents of dibutylboryl triflate. The cooling bath is removed and the reaction mixture is stirred at 25 °C for 1.5 h. The resultant two-phase mixture is cooled to — 78 "C with vigorous stirring. After 1 equivalent of aldehyde is added, the reaction is stirred at —78 °C Tor 0.5 h, and 0 "C for 1 to 2 h. The solution is diluted with diethyl ether, washed with 1 N aq sodium bisulfate, and concentrated. Following oxidation with 30% aq hydrogen peroxide (10 equivalents, 1 1 methanol/water, 0 C. 1 h), extractive workup and chromatographic purification, the aldol adduct is obtained with >99% diastcrcomeric purity. 

Ketones can also be reduced to alkenes via enol triflates. The use of Pd(OAc)2 and triphenylphosphine as the catalyst and tertiary amines as the hydrogen donors is effective.226... 

Vinyl ethers and vinyl esters are not employed extensively in organic transformations. During the synthesis of phlegmarine, however, the stereogenic center at C-10 was to be introduced stereoselectively by catalytic hydrogenation-hydrogenolysis of the vinyl triflate (Scheme 4.7). 

It was envisioned that hydrindanone 83 and cyclopentene 85 could be used as intermediates in the synthesis of e f-retigeranic acid A (1) and e f-retigeranic acid B (2), respectively. To prepare the building block 90, cyclopentene 85 was reduced with diimide (93 %) in order to prevent isomerization and subsequently deprotected with PPTS to yield hydrindanone 90 (quant.), which could provide access to <77/-retigeranic acid B (2) (Scheme 10.7). Hydrindanone 83 was reduced via an enol triflate and then subjected to Pd-catalyzed reduction to provide cyclopentene 91 (87 % from 83). Upon hydrogenation of 91 with Pd/C and cleavage of the acetal with iodine, protected hydrindanone 92 (95 % from 91) was obtained. The deprotection of 92 provided ent-60, whose enantiomer was used in previous syntheses of retigeranic acid A (1) by Corey [14] and Hudlicky [46, 47]. 

Bis(oxazolinyl)pyridine-Ce(IV) triflate complex 78 catalyzed the enantioselective 1,3-DC of acyclic nitrones with a, 3-unsaturated 2-acyl imidazoles. For example, C-phenyl 7V-benzyl nitrone reacted with 77 in the presence of 78 to give the adduct 79 with excellent diastereo-and enantioselectivity. Isoxazolidine 79 was then converted into P -hydroxy-P-amino acid derivatives by hydrogenation of the N-0 bond in the presence of Pd(OH)2/C and cleavage of the 2-acyl imidazole with MeOTf in MeCN <06OL3351>. 

The most versatile approach to disulfonium dications - reaction of triflic anhydride with monosulfoxides of bis-sulfides - has certain limitations in the case of selenium. Most importantly, selenoxides that contain (3-hydrogen atoms are labile.120 122 Trimethylsilyl triflate was used instead of triflic anhydride for synthesis of dication 112 from a selenoxide 111 (Scheme 43).123... 

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