Iminium triflates

With trimethylsilyl iodide 17 the 0,N-acetal 457 gives the iminium iodide as reactive intermediate this converts the enol silyl ether 107 a in situ into the Man-nich-base 669, in 81% yield, and hexamethyldisiloxane 7 [195]. On treatment of the 0,N-acetal 473 (or the N-silylated Schiff base 489) with TMSOTf 20 (or Zny, the intermediate iminium triflate adds to the ketene acetal 663 to give mefhoxytri-methylsilane 13 a and silylated / -amino esters such as 670, which are readily transsilylated by methanol to give the free / -aminoester [70, 196] (Scheme 5.61). 

Treatment of propyne iminium triflate 258 with silylated phosphorus nucleophiles such as Me3SiPPhR affords (3-morpholinoallenyl)phosphanes 259 in high yield (Scheme 8.69) [150]. 

In the presence of AgOTf, the reaction of 1,3,3-triphenylpropadienyl chloride with an amine in CH3CN resulted in the formation of iminium triflate 136 via a 1,2-phenyl shift process [67]. 

In the presence of K2C03, the reaction afforded propargylic amine 137 together with the corresponding iminium triflate 136 [67]. 

An alternative route to tertiary allyl- and propargylamines 145 and 146 is the reaction of Grignard compounds with iminium triflates 147 and 148 (equations 77 and 78). The intermediate iminium triflates 147 and 148 are obtained from the corresponding ami-nals by reaction with Tf20. Primary propargylamines can be prepared from tetraallylated aminals °. 

Selective S-methylation of /V-(trimethylsilylmethyl)thioureas with methyl triflate proceeds smoothly to give the corresponding Af-(trimethylsilylmethyl)iminium triflates in almost quantitative yields.245... 

Cyclization of 2,2 -(naphthalene-l,5-diylbis(oxy))dibenzonitrile to form the dixanthone-iminium triflate 801 occurs upon treatment with trifluoromethanesulfonic acid in good yield. Vigorous conditions are required for the hydrolysis of the dixanthone-iminium triflate 801 and the corresponding xantheno[4,3-c]xanthene-8,16-dione 802 is accessed in modest yield (Scheme 223) <20010L2337>. This approach can also be used to synthesize polymeric dixanthones in moderate yield <20010L2337>. 

The A -unsubstituted nonstabilized azomethine ylides generated from the desilylation of A -[(trimethylsilyl)methyl]-iminium triflates [1384, R = H, R = Ph R R = (CH2)s, (CH2)20(CH2)2] cycloadd to strongly polarized sulfonyl-imines 1385 (Ar = Ph, 4-CIC6H4, 4-O2NG6H4) to produce the corresponding A -imidazolines, for example, 1387, together with the initial cycloadducts 1386 (Scheme 358) <2001H(55)243>. 

N-Silylation with trimethylsilyl triflate forms N-silylated iminium triflates, which are subsequently desilylated in situ with fluoride ion to generate N-silylated azomethine ylides (82TL2589 84CL2041 85CPB1975). 

Reaction of l-chloro-l,3,3-triphenylallene (19) with p-toluidine in the presence of silver triflate gave 2,3,4-triphenylbuta- l-aza-1,3-diene derivative 22a via a novel l, 2-phenyl shift not reported earlier in the solvolysis of allenyl chlorides. The reaction takes place via the formation of the allenyl cation, which is captured as its canonical propargyl cation, first affording the protonated amine 20 (R = Me). Proton transfer from the nitrogen to the acetylenic carbon is followed by migration of a phenyl group in the intermediate vinyl cation 21 (R = Me) to afford the iminium triflate 22a. The latter is hydrolyzed by aqueous sodium hydroxide to the azabutadiene 23 (equation 5). Similar reaction of 19 with aniline and silver triflate afforded the corresponding iminium triflate 22b. ... 

Imino and iminium triflates derived from secondary and tertiary amides respectively, react with l,l,l-2-hydroxymethyl-2-methyl-propane-l,3-dioI in the presence of pyridine to give the OBO derivative [Scheme 2.112]. Primary amides cannot be used as substrates because they dehydrate to the nitrile under the reaction conditions. 

Cyclisation of 2-aryloxybenzonitrile derivatives in CF3SO3H affords xanthone-iminium triflates 36. Vigorous hydrolysis leads to xanthones. The method has been applied to the synthesis of polynuclear dixanthones and a polyxanthone <01OL2337>. 

These salts can react with a variety of nucleophiles including amines (to afford amidines), alcohols (to afford esters), hydrogen sulfide (to afford thioamides), and isotopically labeled water (to afford 0-labeled amides). Iminium triflates are also excellent intermediates for the preparation of assorted heterocycles. Iminium triflates react with azides (to afford tetrazoles), -mercaptoamines (to afford thiazolines), and triols (to afford orthoesters) (eq 58). The reaction of lactams with Tf20 and sodium azide affords tetrazolo-fused bicyclics. ... 

Treatment of unsaturated amides with Tf20 generates intermediate iminium triflates that cyclize under radical conditions (eq 59). ... 

Reaction with Amides. Iminium triflates, readily obtained by the reaction of amides with triflic anhydride, can be reduced to the corresponding amine in the presence of a reducing agent, such as... 

Iminium triflates can also undergo nucleophilic addition with a broad spectrum of nucleophiles. For example, the activated amide can react with malonates in a Knoevenagel-t)tpe condensation reaction (96). Other nucleophiles include, but are not limited to, Grignard reagents to form ketones 56 qj. alkylamines, phosphites, amino acids, pyridines, and pyridine oxydes or alcohols to afford lactones via intramolecular cyclization (97). ... 

The tropane alkaloid skeleton can be accessed in one pot via domino ene-type reactions of acetone silyl enol ether, the first one of them being intermolecular, with catalytic use of TMSOTf (eq 79). Alternatively, as)mmetric tropinones can be reached by cyclization of 1,3-bis-silyl enol ethers with acyl-iminium triflates. ... 

Reaction with Amides. It is well known that treatment of secondary or tertiary amides with Tf20 affords imino and iminium triflates, respectively (eq 57). 

A series of peracetylated Cl-deoxyalditol and C-glycoside dipyrranes were prepared from the corresponding dithioacetal derivatives yields of the pyrrole condensation were reported to be up to 62% (13TL1137). En route to a synthesis of the marineosins, Lindsley utilized a late-stage incorporation of the pyrrole moiety by the nucleophilic displacement of an iminium triflate salt (13TL2231) a related approach was disclosed by Shi et al. (130BC2936). Konduru and Ahmed used pyrrole and indole to open chal-cone epoxides with catalytic amoimts of indium (111) chloride (13SC2008). 

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