Regioselectively addressable

For the cyclization of the less nucleophilic sulfonamides, this conversion can only be achieved via this two-step protocol. The addition of I2 was highly regioselective, addressing the terminal C=C bond, whereas the second step could deliver several products including the SN2-substitution, SN2 -substitution and bimolecular double substitution products 297-299, depending on the length of the tether connecting the amine and the allene moiety [144, 145],... 

Scheme 5 Combined Solid-Phase and Solution Strategy for the Synthesis of Regioselectively Addressable Functionalized Templates (RAFT) with Four Orthogonally Protected Lysine Side Chains for Sequential Attachment of Four Different Peptide Sequences 171...

Other Types of Regioselectively Addressable Functionalized Templates... 

Polymer-Bound Regioselectively Addressable Functionalized Template Molecules... 

Scheme 30 The Immobilization of a Regioselectively Addressable Decameric Template Allows for the Sequential Attachment of Two-Loop Sequences in a Defined Orientation 5153 ...

P. Dumy, I. M. Eggleston, S. Cervigni, U. Sila, X. Sun, and M. Mutter, A convenient synthesis of cyclic peptides as regioselectively addressable functionalized templates (RAFT), Tetrahedron Lett., 36 (1995) 1255-1258. 

Regioselectively addressable functionalized templates (RAFT), oligovalent moieties with chemically distinct functional groups that can be selectively addressed in the preparation of template-associated synthetic proteins (TASP). RAFT are molecular scaffolds that comprise porphyrins, steroids, calixarenes, glycosides, and a variety of cyclic peptides and peptidomimetics. RAFT... 

The catalytic system was subsequently applied to the monoepoxidation of dienes. This was potentially a difficult task, as there was a need to address the issues not only of enantioselectivity, but also of regioselectivity and monoepoxidation versus bisepoxidation. Fortunately, a wide range of dienes could be efficiently monoepoxidized by ketone 1, which meant that a straightforward route to vinylepoxides had been developed (Table 9.1) [9]. 

An impressive indication of the high regioselectivity of hydroxysteroid dehydrogenases (HSHDs) was reported for the oxidation of various hydroxyl groups at the steroid core ofbile acids [26] (Scheme 9.1). The hydroxy-substituents at positions 3, 7, and 12 could be selectively addressed depending on the hydroxysteroid... 

The question of regioselectivity of the cycloaddition with alkylidenecyclo-propanes was also addressed, in analogy with nitrones, and afforded somewhat different results (Table 28) [91, 67b]. 

The first problem to be addressed in the solid-phase assembly of Leb involved the synthesis of the core tetrasaccharide (Scheme 2.17).25 Polymer-bound galactal 10 was epoxidized with DMDO. The resultant epoxide reacted with a solution of glucal 55 to give polymer-bound disaccharide diol 56. This reaction proceeded in a highly regioselective fashion, wherein glycosylation occurred only at the allylic C3 position... 

A detailed study of the mechanism of the enantioselective palladium catalyzed hydrosilylation of styrene with trichlorosilane was carried out with combined QM/MM ab initio molecular dynamics simulations. A number of fundamental mechanistic questions have been addressed, including the main features of the catalytic cycle, as well as the specific nature of the regioselectivity and enatioselectivity. 

The regiochemical reversal induced by the acidic compounds led them to propose the mechanisms illustrated in Scheme 11. In both catalytic cycles, the alkyne linkage inserts into the H-Pd bond the left cycle (no acidic additive) forms linear alkenylpalladium complex, while the right cycle (with HX additive) generates branched alkenyl species. The provenance of the difference in the insertion regioselectivity has not been clearly addressed. 

Seddon and coworkers studied the Friedel-Crafts acylations of toluene, chlorobenzene and anisole with acetyl chloride in [emim][Al2Cl7] and obtained excellent regioselectivities to the para isomer, Scheme 9. Similarly, the fragrance chemical, traseolide, was obtained in 99% yield as a single isomer. Scheme 10. It should be noted, however, that the question of product recovery from the reaction medium still needs to be addressed in these systems. 

However, functional groups, other than a trimethylsilyl group, were not used and complex molecular architectures were not addressed. The regioselectivity for many terminal alkynes is only moderate (R1 = Ph, R2 = H 44 45 = 65 35), whereas the regioselectivity for trimethylsilylacetylene is excellent (R1 = SiMe3, R2 = H 44 45 = 5 95). 

This issue was addressed taking into advance that butyloxycarbonyl (Boc)protection of 249 takes place regioselectively at the oxygen atom to give 252. Subsequent alkylation finds only N-3 accessible for attack (1990S795). Subsequent methanolysis and neutralization afforded the 3-substituted imidazole 1-oxide 228 (Scheme 71). 

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