TIPS group

The greater bulkiness of the TIPS group makes it more stable than the /-butyldi-methylsilyl (TBDMS) group, but not as stable as the /-butyldiphenylsilyl (TBDPS) group to acidic hydrolysis. The TIPS group is more. stable to basic hydrolysis than... 

TIPSCl, pyridine, AgN03 or Pb(N03)2, > 90% yield. These conditions cleanly introduce the hindered TIPS group on the 3 -position of thymidine. 

H2SiF6, TEA, CH3CN, >70% yield. TIPS groups are fairly stable to these conditions. 

PdO, cyclohexene, methanol, 30 min for a primary ROH, 90-95% yield. Secondary alcohols require longer times. The primary TBDPS and TIPS groups are cleaved much more slowly (18-21 h). Benzylic TBDMS ethers are cleaved without hydrogenolysis. ... 

Tris(dimethylamino)sulfonium difluorotrimethylsilicate (TSAF), THF, 0°, 5 h, 64% yield. A TES and two phenolic TIPS groups were also cleaved. 

The bulk of the TIPS group, introduced with TIPSCl (DMF, Im, 92% yield), directs metallation away from the silyl group as illustrated. ... 

Takasu, Ihara and coworkers described an efficient synthesis of ( )-paesslerin A (4-73) using a combination of a [4+2] and a [2+2] cycloaddition (Scheme 4.16) [25], Reaction of 4-71 and propargylic acid methyl ester in the presence of the Lewis acid EtAlCl2 led to 4-72 in 92 % yield, which was converted in six steps into the desired natural product 4-73 by transformation of one of the ester moieties into a methyl group, hydrogenation of one double bond, removal of the other ester moiety, and exchange of the TIPS group for an acetate. 

Muchowski has utilized Af-TIPS-3-iodopyrrole to prepare a series of 3-alkynyl pyrroles 119 using standard Sonogashira conditions [59]. Pyrroles 120 were obtained after fluoride cleavage of the TIPS group. Similarly, 3,4-bis(alkynyl)pyrroles were prepared from N-TIPS-3,4-diiodopyrrole [59]. 

Acetoxylation. Although furans are readily oxidized, furans substituted by a triisopropylsilyl (TIPS) group when treated with DDQ in toluene-acetic acid at 0° undergo acetoxylation at an adjacent a-methylene group.3... 

The dilithiated species 97 can be used to obtain a Ge=Sn doubly bonded species (Equation (182)), which undergoes a thermal isomerization involving migration of the bulky Tip group (Equation (183)).184 The germa-nium/tin compound 108, which contains a fluoride functionality at tin, can be prepared from Mes2GeH2 (Equation (184)), and this can subsequently be converted into the doubly bonded species 109 which can undergo several additional transformations (Scheme 33).226... 

Stereospecific syn addition of methoxysilane to silacyclobutadiene was reported by Fink and coworkers (Scheme 12)72. Ethanol also adds the silacyclobutadiene stereospecifically in a syn fashion to give 42 (Scheme 12), but the ethanol adduct undergoes photoisomerization to a photostationary mixture of 42 and its stereoisomer. A similar system, but with the more bulky 2,4,6-triisopropylphenyl (Tip) groups, also gave the syn ethanol adduct 4373. The rather complicated photochemical-thermal isomerization process was discussed by Fink74. 

Next the generated secondary alcohol is protected as triisopropylsilylether using TIPSOTf. The greater bulk of the TIPS group makes it more stable than the TBS group towards acidic hydrolysis therefore reaction with 5 % H2SO4 cleaves the TBS ether selectively to yield 11. 

The triisopropylsilyl (TIPS) group is introduced under the same conditions as TBS groups.5 Instead of imidazole DMAP can be used, too. Under these conditions only the primary alcohol functionality is selectively protected as TIPS ether. 

An intermediate in the synthesis of laulimalide by Davidson8 illustrates the differential protection of alcohols. The starting materials 56 and 57 already have an alcohol protected as a TBDMS silyl ether and a diol protected as an acetal. The alcohol in 58 is protected as a p-methoxybenzyl ether and the acetal hydrolysed by acetal exchange to give the free diol 60. Selective protection of the primary alcohol by a bulky acyl group (pivaloyl, i-BuCO ) 61 allows silylation of the secondary alcohol with a TIPS group 62. Finally the pivaloyl group is selectively removed by DIBAL reduction to release just one free alcohol 63. 

The nitro-aldols can also be converted to ketones. The enantiomerically pure aldehyde 27 (a protected form of glyceraldehyde) reacts with 28 to give the aldol 29 as a mixture of diastereoisomers. The protecting group R is the very hindered TIPS group (/-Pr)3Si. Dehydration by DCC catalysed by Cu(I) gives the nitroalkene 30 as an E/Z mixture. 

Aldol reactions using catalyst 12 were also performed with water without any organic solvent (Table 2.9) [15]. In these examples, it is assumed that the reaction occurred in the organic phase composed of reactants and the catalyst separated from the water phase. A large excess of ketone was used in these reactions. Catalysts possessing a tert-butyldimethylsilyl (TBS) or a triisopropylsilyl (TIPS) group instead of the tert-butyldiphenylsilyl (TBDPS) group on 12 also effectively catalyzed the reaction with water, but hydroxyproline 2 did not catalyze the reaction under the same conditions this indicated that the hydrophobic substituents of... 

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