Inter- and intramolecular attractions

While much of the emphasis on inter- and intramolecular interactions, secondary bonding, and forces associated with association and dissociation involve attractive forces, we are finding that phobic effects are also important and for some systems are actually the major factors. Briefly, this can be described by the sayings the enemy of my enemy is my friend, or given the choice between bad and worse, bad wins out. Formation of many self-assemblies is due in large measure to such phobic factors. 

Lycorine is an alkaloid that has attracted attention from both the synthetic community and pharmacologists. Prior synthetic approaches have included inter-and intramolecular Diels-Alder cycloaddition. Based on a similar retrosynthetic disconnection, Padwa and co-workers (106,109) chose to use a push-pull carbonyl ylide cycloaddition with a disubstituted pyrrolidinone core to generate a tricyclic substrate. The major difference for this synthetic smdy was the availability of a labile proton a to the carbonyl moiety (Scheme 4.53). 

Cazes et al. reported the Pd-catalyzed intermolecular hydroamination of substituted allenes using aliphatic amines in the presence of triethylammonium iodide leading to allylic amines [19]. In a way similar to the Pd-catalyzed hydrocarbona-tion reactions we reported that the hydroamination of allenes [20], enynes [21], methylenecyclopropanes [22], and cyclopropene [10] proceeds most probably via oxidative addition of an N-H bond under neutral or acidic conditions to give allylic amines. The presence of benzoic acid as an additive promotes the Pd-medi-ated inter- and intramolecular hydroamination of internal alkynes [23]. Intramolecular hydroamination has attracted more attention in recent years, because of its importance in the synthesis of a variety of nitrogen-containing heterocycles found in many biologically important compounds. The metal-catalyzed intramolecular hydroamination/cyclization of aminoalkenes, aminodienes, aminoallenes, and aminoalkynes has been abundantly documented [23]. 

Significant progress in organolanthanide-catalyzedhydroamination over the last two decades has sparked the interest in the development of analogous catalytic hydrofunctionalization protocols. Catalytic hydrophosphination of unsaturated carbon-carbon linkages offers an attractive atom-economic route to phosphines [87,177], It should be noted that inter- and intramolecular hydrophosphinations are also... 

The chemistry of protein fibres, especially that of wool, is more complex than that of most other types of fibre. The amide groups which link the repeat units are also to be found in nylon fibres. Amides can be cleaved hydrolytically by strong acids and bases. However, the inter- and intramolecular bonds in wool are particularly numerous. There are hydrogen and disulphide bonds, salt links and hydrophobic attraction. All of these bonds are important for understanding chemical damage to wool and the possibilities for its detection. 

With the same goal of less conformational freedom and stronger inter-and intramolecular jt-overlap, a new fused compound, bis(dithienothiophene) (BDT, lla)[96-98] and its fused counterpart pentathienoacene (PTA, llb)[99] have been synthesized (Figure 3.1.4). PTA is attractive because it combines the molecular shape of pentacene with a thiophene monomer. The linear condensed thiophene backbone not only imparts extended Jt-conjugation, but is also more planar than BDT. OTFTs of 11a yielded high mobilities of 0.05 cm V s with a high on/off ratio of 10, ... 

Many-electron theory gives the van der Waals attractions at all r both for inter- and intramolecular cases with no assumptions concerning overlap. It does not necessitate different starting points, or different theories, one for large r and another near r. It covers smoothly the difficult intermediate region. 

Hydrogen bonding A strong inter- or intramolecular attraction that occurs between hydrogen and oxygen atoms. 

In Fujiwara s interesting arene activation chemistry, oxidative addition of an arene CH bond to Pd, specially fast for electron-rich arenes, is followed by a Heck-like insertion of an alkene to give a vinylated arene as product. Arenes undergo unexpected selective trans hydroarylation with both terminal and internal C=C double bonds, both inter- and intramolecularly, with turnover numbers up to 4500, giving the thermodynamically less favorable cis-alkenes. The simplicity, generality, and efficiency of this process could be very attractive for possible industrial application (Eq. 2.48) [133]. 

Titanium-catalysed inter- and intramolecular hydroamination of olefins and allq nes is an attractive carbon-heteroatom bond-forming reaction as it is 100% atom economical (Scheme 5.5). As hydroamination reactions catalysed by early transition metals and main-group metals have been recently re-viewed, we will only cover titanium-catalysed hydroamination reactions since 2014. 

Cyclopropanation of alkenes, in both inter- and intramolecular modes, constitutes an attractive route to polycycloalkanes. These cyclopropanations of alkenes are carried out through car bene or carbenoid intermediates . For the direct cyclopropanation of alkenes, the methylene iodide zinc-copper couple (Simmons-Smith reaction)reagent is commonly used. Several modifications of this procedure, including acceleration with ultrasound, are known °°. A somewhat less frequently used procedure for cyclopropanation is through methylene addition from diazomethane, which can be carried out either thermally or photochemically or in the presence of metal salts, e.g. Pd(OAc)2 or Rh2(OAc)4. In Table some examples of the preparation of cyclopropane bearing... 

Hydroamination of 7i-bonds is one of the most straightforward methods for the construction of C N bonds and, as such, has attracted a lot of attention. NHC- Au catalysts, in line with results obtained in hydration and hydroalkoxylation reactions (vide supra), proved highly efficient in this field and the inter-and intramolecular hydroamination of various alkenes," allenes," and alkynes" were reported with a number of NHC- Au complexes. Among these reports, Widenhoefer published an elegant bis-hydroamination of allenes, leading... 

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