Derivatizations monosubstitutions

Derivatization of some mono(cyclopentadienyl) complexes to yield new monosubstituted species can often be accomplished by metathetical exchange (Equation (26)) or protonation reaction.295 Protonolysis of (CsPr 4H)Ca[N(SiMe3)2](THF) with several terminal alkynes HC CR in either toluene or hexanes produces the... 

Dianions of A -monoprotected glutamic acid esters are very useful intermediates for y-monoalkylation leading to y-monosubstituted glutamic acids (such as 52, 53 Scheme 19).[94] Among them, y-allyl-substituted glutamic acid 52 (R1 = CH2CH=CH2) can be derivatized into y-substituted homoproline 56 (Scheme 20). 

The preparation of most monosubstituted and many polysubstituted metallocenes (especially ferrocene derivatives) is now routine, and extensive reviews of synthetic methods have been published.4-5 In brief, one of four approaches is used to produce derivatized metallocenes (1) a... 

Cyanuric chloride on monosubstitution with nucleophiles such as methanol or 4-amino-azobenzene followed by displacement of a second chlorine with alanine amide gave compounds which are used for precolumn derivatization of amino acids. The diastereoisomers formed are resolved by reverse-phase HPLC <92MI 6l2-0i>. Enantiomeric amino acids are separated by HPLC on bis[carbamoyl(alkyl)methylamino]-6-chloro-l,3,5-triazine derived stationary phases <93JC277>. 

At present silylation of amines is a well-investigated, but relatively rarely used, method for their derivatization owing to the facile hydrolysis of the resultant iV-TMS compounds. It leads to the formation, in the reaction mixtures, of both mono-(RNHTMS) and h -[RN(TMS)2] derivatives. This multipUcity of products from the same precursor presents some difficulties in data interpretation. The N-(tert-butyldimethylsilyl) (TBDMS) derivatives are more resistant to hydrolysis, and their formation is unambiguous (only N-monosubstituted compounds are formed) because of steric reasons.It is interesting to note that one of the numerous sUylating agents (see Table 3 in Hydroxy Compounds Derivatization for GC Analysis, p. 1165)—trimethylsilyl imidazole—possesses a unique selectivity, because it is inert in relation to amines. 

Starch derivatized by reaction with ethene oxide has been hydrolysed and silylated, and the distribution of the hydroxyethyl groups in the modified D-glucose units determined by gas chromatography. Six monosubstituted and twelve disubstituted forms were completely separated and identified from their mass spectra. 

Nonetheless, derivatization methods have been successfully employed [56-58,65], most notably via use of the diazonium salt of 4-nitroaniline, For instance, in the study of phenylamide pesticides, no resonance was observed from these colorless compounds however, after derivation to azo dyes, detection limits of (2-4) X 10 M were achieved for monuron, diuron, a-napthylacetamide, and /3-napthylacetamide. Selectivity in distinguishing derivatized products from isomers of monosubstituted phenols (i.e., ortho, meta, and para) has also been shown to be successful, as illustrated in Fig. 8. Moreover, coupling the sensitivity and selectivity of RRS to the well-known spot-test method (qualitatively identifies colorless solutions only by visual identification of the colored products), a more accurate and sensitive characterization method of trace organic compounds is achieved. Such work has been conducted by Nakamura et al. in the characterization and detection of phenols and heterocyclic aromatic compounds on fruit rinds and food preservatives [58]. 

While the original Wynberg and Staring approach was limited to parent ketene and either electron-deficient aldehydes or ketones, Tennyson and Romo have expanded the scope and practicality of this process by the use of in situ generated monosubstituted ketenes [29]. The use of less reactive dichlorinated aldehydes 44 was also demonstrated, with the utility of the (3-lactone products 45 showcased via a range of derivatization strategies, including conversion to the (3-hydroxy ester 46 (Scheme 3.8). 

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