Ferf-butyldimethylsilyl triflate

The key step in a short synthesis of ( )-tylophorine77 is an intramolecular double conjugate addition reaction. Reaction of the ( , )-unsaturatcd ester 1 (R2 = 8-phcnylmcnthyl) with ferf-butyldimethylsilyl triflate in the presence of excess of triethylamine in dichloromethane produces an 80 20 inseparable mixture of the indolizidines 2A and 2B78. Treatment of a mixture of 2A and 2B (R2 = 8-phenylmethyl) with sodium hydride in refluxing tetrahydro-furan for 2.5 hours gives the single indolizidine 2 A. Dioxanyl ester 1 furnishes, on reaction with... 

Deprotection of the spiroketal protected porphyrazines to generate the pz-diols proved difficult because the desired product is easily oxidized before isolation or derivitization. It was therefore anticipated that the high electron density of the de-protected pz-diol would be reduced by core-metalation, so attempts were made to deprotect ketal 193 with TFA to give enediol 201. However, 201 rapidly decomposed during purification attempts. To avoid this problem pz (201) was trapped with terl-bu(yIdiinc(liyIsi IyI triflate to give the ferf-butyldimethylsilyl derivative 202 (79%) as a stable compound (Scheme 40) (10). 

Substituents can be introduced even at the lateral 4-position (1993JCS(P1)625). In the example shown in Scheme 122, the reactive 5-position is first protected by silylation effected by abstraction of the proton at C5 using a strong non-nucleophilic base like LiTMP, followed by treatment with TMS chloride. With the 5-position thus protected subsequent O-silylation of 431 to give 432 activates the lateral proton at the 4-position, which is removed by a second equivalent of base. The lateral anion 433 is then quenched with an electrophile like ferf-butyldimethylsilyl (TBDMS) triflate that produces 434. The entire sequence 430 -> 434 can be preformed in one pot. 

In the rearrangement of allyl fluoroacetates, trialkylsilyl triflates have been introduced as a new reagent for the Z-selective generation of silyl ketene acetals485. Thus, when (T)-crotyl fluoroacetates are treated at ambient temperatures with a trialkylsilyl triflate in the presence of a tertiary amine, rearranged products with a svn relationship are preferentially obtained. The ketene acetal intermediates cannot be isolated and the geometry has been deduced from the stereochemistry of the products. The selectivity of this process improves in the order triisopropyl > ferf-butyldimethylsilyl > rerf-hexyldimethylsilyl > trimethylsilyl a triethylsilyl (see Table 11). 

Additionally, primary amides and ketoamides were synthesized in good yields via a more traditional carbonylation-deprotection sequence in the presence of Pd(OAc)2/2PPh3 (Scheme 2.13) [134]. Initially, aryl iodides were reacted with ferf-butylamine under 1 bar of CO. When the reaction proceeded at 60 °C, ketoamides resulting from double carbonylation were mainly produced, whereas formation of the amides was favored at 100 °C. The desired primary amides were produced after heating the previous isolated products with one equivalent of tert-butyldimethylsilyl triflate (TBDMSOTf) in toluene at 100 °C. 

Conjugate Addition of Alkynylzinc Bromides. Alkynylz-inc bromides undergo conjugate addition with a, 8-unsaturated ketones in the presence of ferf-butyldimethylsilyl trifluo-romethanesulfonate or TIPS triflate (trimethylsilyl trifluo-romethanesulfonate is also effective) in ether-THF at —40 °C to give the corresponding 1,4-adducts (54-96% yields). A representative example is illustrated in eq 7. 

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