Polyfunctional building blocks

Scheme 4.27 Synthesis of Brook rearrangement substrate 136 featuring a three-step synthesis of polyfunctional building block 166...

The combination of pept(o)id-introducing MCRs with subsequent and efficient post-condensation transformations, especially ring-closing protocols, is an efficient concept to produce (cyclic) pseudopeptides. The most important versions make use of protected or convertible functional building blocks to allow later condensation, specially cycfization. Most relevant are Ugi-deprotection-cyclization (UDC), Ugi-activation-cyclization (UAC), and the Ugi-deprotection-activation-cycfization (UDAC), which take advantage of the diverse functionalities incorporated into the previously synthesized MCR-adduct as bi- or polyfunctional building block (Fig. 3) [15, 16]. 

The same strategy can be used with polyfunctional building blocks, and a variety of peptoid-based cryptands, cages, and cryptophanes was synthesized (Scheme 26) [100]. 

Enophile activation by an alkoxy substituent was also observed with the particularly smooth and cis stereospecific additions of dialkylallylboranes (43) to ethoxyacetylene (44).The resulting dienylbo-ranes (45) are interesting polyfunctional building blocks and provide 2-ethoxy-1,4-dienes (46) or 1,4-enynes (48) (75-81%) by protonolysis or alumination/elimination (Scheme 10 Table 6). 

Ganesh, R Nicholas, K. M. 1997. Reactions of cobalt-complexed acetylenic aldehydes with chiral (Y-alkoxyallyl)boranes Enantioselective synthesis of 3,4-dioxy 1,5-enynes and stereoselective entry to polyfunctional building blocks. 7. Org. Chem. 62 1737-1747. 

Polyfunctional organomercurials have emerged as useful building blocks for the construction of supramolecular species. Compound 137, for instance, was shown to complex benzene, yielding extended binary stacks where the two components alternate (Figure 25).235 These stacks are rather compact (centroid distance of 3.24 A), so that secondary 7t-interactions occur between the benzene molecule and the mercury centers. Each of the six C-C bonds of the benzene molecule interacts with one of the six mercury centers of the two juxtaposed molecules of 137. As a result, the benzene is hexacoordinated in a fashion. The strength of the Hg-C interactions must... 

Based on the Kulinkovich reagent (Ti(OiPr)4/iPrMgCl), a new route to allyltita-niums has been devised by Sato and coworkers and this has allowed the synthesis of chiral allylTi reagents which, by reaction with aldehydes and imines provide diverse polyfunctional chiral building blocks. Thus, while a number of versatile and dependable Ti-based allyl-transfer reagents are now available, the development and employment of chiral allyltitaniums appears to be poised for new application. 

All BMI building blocks and maleimide-terminated oligomers discussed previously are synthesized from the corresponding polyamine precursor and maleic anhydride simply because of economic reasons. However, there are other synthetic methods available, for instance, the reaction of a functionalized monomaleimide with a polyfunctional monomer or oligomer. Such a functionalized monomaleimide is maleimido benzoic acid or its acid halide. These were used to synthesize maleimide-terminated polyamides (39, 40) or polyesters (41), respectively. 

The selective preparation of various chlorophosphines used as building blocks for the preparation of polyfunctional phosphines is achieved using dichloro (diethylamino)phosphine (Et2NPCl2). Alkylation of this phosphine with organozinc halides furnishes, after borane treatment, protected aminodi-organophosphines. These in turn can be converted to the corresponding... 

Alkynylation of zinc-copper compounds has been used for the synthesis of polyfunctional acetylenic ethers [84] and for the preparation of building blocks for pharmaceutically active compounds [85]. Whereas cross-coupling between non-activated iodoalkenes and zinc-copper reagents only proceeds at elevated temperatures and in polar solvents such as NMP or DMPU (60 12 h) [86], alkenyl... 

The accessibility of the fullerenes [1] in macroscopic quantities [2] opened up the unprecedented opportunity to develop a rich three-dimensional chemistry of spherical and polyfunctional all carbon molecules. [3-8] A large multitude of fullerene derivatives like exohedral covalent addition products, salts, cluster opened and defined degradation products, heterofullerenes and endohedral derivatives can be imagined and numerous examples, especially of covalent adducts have been synthesized and characterized. [3-8] Within a few years the fullerenes became essential building blocks in organic chemistry. Most of the chemistry of fullerenes has so far been carried out with Ceo (1) with little work on C70 and few experiments with C76 and Cg4. This is simply due to the fact that Ceo... 

Based on our studies of conjugated azoalkenes over nearly twenty years, these starting materials have been shown to represent useful building blocks for the construction of uncommon polyfunctionally substituted pyrrole f93MI4611 or pyrazole heterocycles. 

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