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Alcohol selective silylation

Silylation, Tritylation, and Sulfinylation of Alcohols. Tritylation, including selective tritylation of a primary alcohol in the presence of a secondary one, silylation of tertiary alcohols, selective silylation to i-butyldimethylsilyl ethers, and sulfonylation or sulfinylation of alcohols proceed more readily in the presence of DMAP. Silylation of /3-hydroxy ketones with Chlorodiisopropy-Isilane in the presence of DMAP followed by treatment with a Lewis acid gives diols (eq 4). ... [Pg.170]

Scheme 5 details the asymmetric synthesis of dimethylhydrazone 14. The synthesis of this fragment commences with an Evans asymmetric aldol condensation between the boron enolate derived from 21 and trans-2-pentenal (20). Syn aldol adduct 29 is obtained in diastereomerically pure form through a process which defines both the relative and absolute stereochemistry of the newly generated stereogenic centers at carbons 29 and 30 (92 % yield). After reductive removal of the chiral auxiliary, selective silylation of the primary alcohol furnishes 30 in 71 % overall yield. The method employed to achieve the reduction of the C-28 carbonyl is interesting and worthy of comment. The reaction between tri-n-butylbor-... [Pg.492]

Primary alcohols are selectively silylated by 1 and N(C,H5)j in CH,CU at 25°. Silylation of secondary alcohols is effected by catalysis with DMAP, and even tertiary alcohols can be silylated by 1 in DMF catalyzed by DMAP. [Pg.59]

Selective silylation. Hexamethyldisilazane alone can effect silylation, but only at elevated temperatures. Rapid silylation of amines, alcohols, and acids can be achieved at 0° in CH2C12 if chlorotrimethylsilane is also present. Selective silylation is also possible by adjustment of the proportions of HMDS and TMSCl. Thus only... [Pg.175]

Many transition-metal complexes have been reported as catalysts of this reaction, including [lr(g-Cl)(coe)2]2 [74] and [lrH2(solv.)(PPh3)][SbF6] [75]. The latter catalyst appeared to be a very active and highly selective. The hydroxyl group can be selectively silylated, even in the presence of other potentially reactive C=C and C=0 groups. The order of relative reactivities of alcohol isomers is secondary alcohol > primary alcohol > tertiary alcohol. [Pg.361]

Diels-Alder cyclization of IfiAO-undecatrienals.5 These unsaturated aldehydes undergo intramolecular Diels-Alder cyclization, particularly under Lewis acid catalysis. The reaction is highly endo-selective. Silyl-protected alcohol groups at C4 and Q can be present, and t-butyldimethylsilyl ethers show a strong axial preference. [Pg.6]

Selective Oxidation of Primary Alcohols via Silyl Ethers... [Pg.338]

The protection of alcohols as silyl ethers has been reviewed62, as have the relative stabilities of the different trialkylsilyl groups63. Their stability under alcohol oxidation conditions and their oxidative deprotection have been discussed64. Methods for selective deprotection of the various silyl ethers have been the subject of an excellent review65. [Pg.1674]

Naiki, M. Shirakawa, S. Kon-i, K. Kondo, Y. Maruoka, K. Tris(2,6-diphenylbenzyl)amine (TDA) and tris(2,6-diphenylbenzyl)phosphine with unique bowl-shaped structures synthetic application of functionalized TDA to chemo-selective silylation of benzylic alcohols. Tetrahedron Lett. 2001, 42, 5467-5471. [Pg.129]

Step 2 Selective silylation of the least hindered 1 ° alcohol. [Pg.57]

After library synthesis and solid-phase assay of 100,000 beads on a red-labeled synthetic receptor [23], 55 deep staining beads were selected and their code was released via photolysis at 350 nM the released alcohols were silylated with N, O-bis(trimethylsilyl) acetamide and injected into a capillary GC with EC detection decoding 52 different structures, which are shown in Figure 9.7. [Pg.200]

UButylmethoxyphenylsilyl ethers (r-BMPSi ethers). In DMF in the presence of NfCjHj), this bromosilane reacts with primary, secondary, and tertiary alcohols to form silyl ethers in good yield, and also with some enolizable ketones to form enol silyl acetals. Selective silylation of primary alcohols is possible by use of CHjClj as solvent. The hydrolytic stability of these ethers is intermediate between that of t-butyldimethylsilyl ethers and that of t-butyidiphenylsilyl ethers. The most useful feature of this new protecting group is the selective cleavage by fluoride ion in the presence of other silyl ethers. [Pg.101]

The epoxy alctrfiol (97), a key intermediate in the synthesis of maytansine, has been prepared through Ti-catalyzed epoxidadon of (95 equation S6). The alcohol (95) exists predominantly in confoimation (162), with the allylic hydrogen at C-4 and the ir-bond very nearly eclipsed. The oxygens of the alcohol and silyl ether which are located below the plane the ir bond complex with Ti this complex blocks the approach of the epoxidizing reagent fitom the a-fu and hence the P-epoxide is fmmed. It is of interest to note that the ir-facial selectivity resulting fiom this route is the opposite of the ir-facial selectivity observed in MCPBA epoxidadon (see equadon 33). [Pg.380]

Reductive ozonolysis of the double bond of the appropriate epimer of 36, followed by selective silylation of the diol produced, and radical deoxygenation of the secondary alcohol function, lead to 37, which is a derivative of the cyclohexyl unit of the immunosuppressive agent tacrolimus [20]. [Pg.295]

TBDPS ether is visible under UV light and thus it is more advantageous than the corresponding TBDMS ether if there is no chromophore present in the alcohol. Selective protection of the primary alcohol can be achieved as shown below. Silyl chloride and cleavage by-product silylol are both lachrymators and therefore the reactions should be carried out in the hood. The procedures for protection and cleavage are applicable to other silyl ethers such as ferf-butyldimethylsilyl, trimethylsilyl, and tri-isopropylsilyl. [Pg.196]

The Ireland contribution to nonactic acid synthesis, outlined in Scheme 4.32, involves a selective silyl ketene acetal formation and Claisen rearrangement in the key step. D-Mannose (209) was readily converted in a straightforward manner to dihydrofuran 212 via 210 and 211 in 36% overall yield. Esterification of the free alcohol with propionyl chloride followed by the an enolate Claisen rearrangement afforded a mixture (89 11) of tetrahydrofuryl propionates 213 after catalytic reduction. [Pg.131]

L-Arabinose reacts differently than o-xylose with acetone and gives a pyrano-side instead of a furanoside. Thus an alternative route to 18 was sought that can be applied both to o-xylose and L-arabinose [59]. It starts with the selective silylation of HO-C(5) [60], then acetonide formation protects alcohols moieties at C(l) and C(2). Subsequent benzylation of HO-C(3), hydrolysis of the silyl ether, and iodination provides 18 from o-xylose and 19 from L-arabinose (Scheme 7). Zinc reduction of 19 generates enal 20, but not the reduction of 18 [61]. Thus 18 and 19 are converted first into their methyl furanosides 22. The latter are reduced with Zn into... [Pg.91]

Selective silylation of alcohols.1 The reagent selectively silylates equatorial hydroxyl groups in quantitative yield within 4-10 hours at room temperature. Axial hydroxyl groups do not react under these conditions. [Pg.364]


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See also in sourсe #XX -- [ Pg.236 ]




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