Linkage traceless

In contrast to Si and Ge linkages (traceless linkers) of the aryl ring to the resin where electron-rich aromatic ring systems favor rapid cleavage, the reductive cleavage of arylsulfonates works well with electron-poor aromatic rings. 

Traceless linkages leave no obvious site of attachment to support upon synthesis completion and are... 

Recently, palladium-catalyzed carbonylation of chloropyrimido[4,5-d]pyrimidines has been reported (Equation 51) <2006W0065703>. Raney nickel-mediated desulfurization of alkylthiopyrimido[4,5-, pyrimidines was described in GHEC(1984), and has been applied recently both in the desulfurization of reduced species (Equation 52) <2001WO64679> and for cleavage of sulfur linkages in traceless solid-phase synthesis <1999BMCL965,... 

Linear polarization, and NLO properties, 12, 102 Linear polymers, siloxanes, synthesis, 3, 660 Linkage isomerism, for photochromic behavior, 1, 245 Linked cages, metallacarboranes, 3, 245 Linkers, traceless, chromium carbonyls as, 5, 251 Lipids, in bioorganometallic chemistry, 1, 904 Liquefied noble gases, in low-temperature infrared studies, 1, 264... 

The most prominent anchors for traceless linkage of arenes are based on silyl linkers. Generation of a diverse benzodiazepine library [40] has clearly shown the advantages of this type of detachment because no additional functionality, which might bias the library, was preserved in the final molecules (Scheme 6.1.33). 

Aminopyrimidine. Early representative examples of a sulfone traceless linker were demonstrated by Villalgordo et al. and Gayo and Suto in the synthesis of 2-aminopyrimidines. The sulfur linkage was obtained by treating Merrifield resin with thiourea to provide the isothiouronium salts 1 (Scheme 12.5). Condensation of 1 with acetylenic ketones 2 or malononitrile derivatives 3 yielded the pyrimidine skeleton 4. Oxidation of the alkylthio linkage with mCPBA provided the corresponding sulfone derivatives that underwent nucleophilic substitution with various amines to form 2-aminopyrimidines 5. 

The third t)tpe of linkage (solid support-O-Si-C-) is called a traceless linker after cleavage, the substrate is released in an unmodified form, which means that the silicon atom is replaced with a hydrogen atom. An example is shown in eq 16. The substrate 25 was lithiated and then silylated with i-Pr2SiCl2 to give a chlorodi-isopropylsilyl intermediate in 71% yield this was next attached to 4-hydroxylmethyl polystyrene (26) to give 27. The ultimate... 

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