Extending the Chemistry

It was quickly realized that the SCF reactor was not restricted to hydrogenation reactions and could, in principle, be adapted to any type of solid or supported catalyst Successful reactions included Friedel-Crafts alkylation [36], etherification [37], hydroformylation [38], and base-catalyzed transesterification [39], 

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Youngs and co-workers extended the chemistry toward synthesizing water-soluble silver carbene complexes 68a-68c (Figure 28) by using hydroxyl-containing pincer-type iV-heterocyclic carbenes as ligands.1 4 It is interesting... 

In the interim period, results have accumulated steadily, in endeavors to address and extend the chemistry beyond the initial perceived limitations. These limitations include the following (a) the effective catalytic syntheses are confined to the reactions utilizing catecholborane (b) the scope of alkenes for which efficient rate, regio- and enantio-selectivity can be achieved is limited, and (c) the standard transformation mandates the oxidation of the initially formed (secondary) boronate ester to a secondary alcohol, albeit with complete retention of configuration [8]. Nonetheless, for noncatalytic hydroboration reactions that lead to the formation of a trialkylborane, a wide range of stereo-specific transformations may be carried out directly from the initial product, and thereby facilitate direct C-N and C-C bond formation [9]. 

Trimethylindium and B2H6 yield a solution of In(BH4)3, which can be obtained as the THF adduct, which decomposes in vacuo. The aluminohydride analogue In(AlH4)3 is even more unstable,1 and there seems to be little chance of extending the chemistry of indium(III)-hydrido systems. 

The advent of the polyether antibiotics with the challenging aspect of stereocontrolled construction of the substituted tetrahydrofuran units has greatly extended the chemistry of this oxygen heterocycle. The nonactins (194), lasalocid A (195) and monensin (196) are among the ionophores for which syntheses have been achieved. Detailed reviews on synthesis of reduced furans are available (65HOU(6/3)l, 80H(14)1825). 

Even more important point to note is that often times one cannot even extend the chemistry of the same molecule in the same medium under different conditions. The best examples are found in the crystalline state where molecules tend to crystallize as different polymorphs. It has been very well established that the different polymorphic forms of a compound show significant differences in photochemical behavior. A classic example that shows polymorphic form dependent reactivity is cinnamic acid. Substituted cinnamic acids crystallize in three polymorphic forms namely a, (3, and y and provide photodimers characteristic of the crystal packing (Sch. 1). One of the interesting crystal structure dependent cyclizations is that of tetrabenzoyl-ethylene [143]. Photolysis of only one of the two dimorphic modifications gives rise to a product while the other is inert to UY radiation (Sch. 25). 

The efficiency of HRP for the coupling of iodotyrosine derivatives has also been studied by Eickhoff) who extended the chemistry to include the formation of biaryl linkages between small peptides in low yields (5-6 %) [30]. Biaryl-containing peptide libraries were also prepared by HRP oxidative coupling of appropriate phenolic precursors. 

Dangschat and Fischer" have most elegantly extended the chemistry of the cyclitols by an investigation of the naturally occurring cyclitol, conduritol (XXIV). This optically inactive substance was discovered in... 

Attempts to extend the chemistry described in the previous section to group VIII propargyl metal complexes afforded considerably different products, and in some cases no allenyl-containing carbonyl complexes could be isolated. 

What allows us to see the uncommon oxidation states is their particular environment in terms of groups or atoms bound to the metal ion, and in general there is a close relationship between the groups that coordinate to a metal and the oxidation states it can sustain, which we will explore later. The definition of common in terms of metal complexes in a particular oxidation state is an ever-changing aspect of coordination chemistry, since it depends in part on the amount of chemistry that has been performed and reported over time, a metal in a particular oxidation state may change from unknown to very rare to uncommon as more chemists beaver away at extending the chemistry of an element. At... 

Two new reports extend the chemistry of fluorinated vinyl organometallies. In the first, trifluorovinyllithium is shown to be much more stable in Et20 (up to -30°C) than in THF.24 Remarkably, the other research paper by the same group reports that the... 

We have extended the chemistry shown in Scheme 10 to the preparation of e f-nangustine (ent-99) and to the synthesis of compound 119 that corresponds to the structure assigned to montabuphine [51]. Montabuphine has attracted considerable attention because its isolation suggested that both enantiomeric forms of the montanine alkaloid framework occur in nature. In the event, and by employing a reaction sequence similar to that shown above, we were able to prepare target 119 from cis-l,2-dihydrocatechol 100. However, a comparison of the physical and spectral data recorded on the synthesised form of amine 119 with those reported for (+)-montabuphine suggests that they are different compounds. 

The development of polyurethane adhesives can be traced back more than 60 years to the pioneering efforts of Otto Bayer and co-workers. Bayer extended the chemistry of polyurethanes initiated in 1937 [1] into the realm of adhesives about 1940 [2] by combining polyester polyols with di- and polyisocyanates. He found that these products made excellent adhesives for bonding elastomers to fibers and metals. Early commercial applications included life rafts, vests, airplanes, tires, and tanks [3]. These early developments were soon eclipsed by a multitude of new applications, new technologies, and patents at an exponential rate. 

Complexes of the general form /ac-Re(C0)3(amine)2(halide) have been widely studied in the past few years mainly because of their remarkable catalytic properties. Abel and coworkers have extended the chemistry of these compounds a little further by using 2,2 -6 ,2"-terpyridine as a fluxional bidentate amine. The dimethylbismolyl ligand has been used to synthesise (dimethylbismolyl)Mn CO). ... 

A new non-stereospecific route to cyclopropanes involves the copper(n)-halide-catalysed addition of bromomalonic acid to an alkene in the presence of an amine. Meanwhile, Chan has extended the chemistry of l,5-bis(trimethyl-silyloxy)-l,5-dimethoxypenta-l,4-diene (3), which, upon reaction with Lewis... 

The few studies on Sm(Tp 2)2 presented herein show that unique structure of this reduc-tant is likely responsible for its unusual reactivity and subsequent isolation of unique reaction products. Further studies of this and similar reductants utilizing pyrazolylborate ligands will likely lead to novel reactions and greatly extend the chemistry of Sm(II). 

The asymmetric allylic phosphination of allylic acetate derivatives proceeded under mild conditions to afford chiral phosphines in good to excellent yields (Scheme 4.10) [26]. The catalyst system was comprised of commercially available materials including a common palladium source and JosiPhos as the chiral ligand. The enantioselectivity of the process was outstanding (up to 96% ee), and the conditions were quite mild (40 C). While only a single alkyl phosphine was screened, these results provided the proof of concept for the process, and extending the chemistry to more complex substrates and phosphorus... 

Fluoromethylidyne and Difluoromethylidene. Bismethylidyne complexes of iron are themselves somewhat rare. For example, when Lentz and co-workers first prepared nonacarbonylbis( i3-fluoromethylidyne)triiron, [Fe3(CO)9( X3-CF)2] (137), it was only the second known compound to contain the Fe3(CR)2 moiety. Since then, Lentz has extended the chemistry of this compound by studying (1) its reactions with alkynes (138-140), a phosphaalkyne (140,141), and Lewis acids (140,142), (2) its carbonyl substitution chemistry with nitriles and phosphines (143),... 

Obviously these isolobal comparisons can be made for any compound of boron. Systematic application of the analogy in boranes will definitely unearth a lot of new chemistry, extending the chemistry of the boranes to other systems. 

Lee-Ruff and co-workers have continued their interest in the photochemistry of cyclobutanones. Specifically, they have profitably extended the chemistry of the oxacarbenes by trapping these intermediates with selected amines, to good effect Thus, the Canadian team photol) ed the ketones 4 and 5 in the presence of purines as well as water and alcohols to produce the corresponding nucleoside analogs, lactols, and acetals, respectively (Scheme 6 and Table 49.1). 

Concurrent with the product developments, carried out primarily in ParUn, NJ, there were developments at the DuPont Experimental Station, particularly by Pazos and Nacci in extending the chemistry of these systems. Much of this work is buried in the patent literature and is herewith presented to illustrate the approaches considered. 

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