Synthetic accessibility

The synthetic accessibility of ligands designed by de novo methods. This topic typically is not considered. Some compounds with unstable or reactive function-ahties are eliminated by applying simple rules, but these rules are still insufficient. 

The reaction between ethyl chloroformate and 2-aminothiazoles provides easy synthetic access to thiazolyl 2-carbamaies (269) (Scheme 163)... 

Workers at SmithKline Beecham extended the synthetic access to interesting mono- and di-substituted oxazoles through an improved procedure for aryl-substituted... 

The repertoire of a-amino acids used by nature in the biosynthesis of proteins is limited to about 20 structures. Since the diversity of synthetically accessible a-amino acids is enormous, initial studies have been undertaken to investigate the possibilities offered by incorporation of noncoded amino acids into en2ymes. Some selected examples of successful modifications are presented below. 

Oberhuber, M. and Krautler, B., Breakdown of chlorophyll electrochemical bilin reduction provides synthetic access to fluorescent chlorophyll catabolites, Chembio-chem, 3, 104, 2002. 

Second, every compound with a Group 14-Group 16 element double bond corresponds to a minimum on the potential energy surface, as confirmed from all positive eigenvalues of the Hessian matrix. This suggests that all the double bond compounds in Table I are synthetically accessible, if one can find an appropriate synthetic methodology. 

The reduction of a high-valent metalla-calix[4]arene in the presence of olefins, dienes, and acetylenes is probably the best, though not unique, synthetic access to the corresponding complexes. A few significant examples have been so far reported. 

A different synthetic access to a 1 -metallacyclopropene, which can be a versatile organometallic synthon, is displayed in Scheme 33. The mono-alkyne derivatives of W(IV)-calix[4]arene are easily accessible through the thermal displacement of cyclohexene from 32 using the appropriate acetylenes. The reaction led to complexes 34 and 172-174. The proposed 3-metallacyclopropene has been confirmed from the spectroscopic and the X-ray data. The H NMR data reveal a cone conformation of the calixarene with a four-fold symmetry, for which the... 

Dendronized polymers are a subclass of comb polymers [7]. The synthetic access to comb polymers with dendrons in the side chain is somewhat more difficult and time consuming compared to most other polymers of this class. It is therefore not too far fetched to ask whether the exciting properties described above... 

The phenanthrene 1,2- and 3,4-diones are synthetically accessible from the related 8 phenols. Oxidation of 2-phenanthrol with either Fremy s salt ((KS0 )2N0) or phenylseleninic anhydride gave phenanthrene 1,2-dione directly (55). Unexpectedly, oxidation of 3-phenanthrol with (KSOg NO yielded 2,2-dihydroxybenz(e)indan-l,3-d-ione (Figure 10). However, phenanthrene 3,4-dione was readily obtained from 3-phenanthrol by Fieser s method entailing diazonium coupling, reduction, and oxidation of the resulting 4-amino-3-phen-anthrol with chromic acid (56). 

More convenient synthetic access to 15 is provided by the sequence in Figure 13 (68). Alkylation of the potassium salt of 2,6-dimethoxy-1,4-cyclohexadiene with 2-(2-naphthyl)ethy1 bromide in liquid ammonia followed by mild acidic hydrolysis generated the diketone (16). Cyclization of 16 in polyphosphoric acid took place smoothly in the desired direction to afford the partially saturated ketone which underwent dehydrogenation with DDQ to 15. 

L = axial ligands, n = 0, 1, 2) have been extensively investigated regarding their specific electronic, chemical, and physical properties [4], Particularly, oxo-centered triruthenium cluster complexes with bridging acetates attracted the most attention owing to their synthetic accessibility, multiple redox behavior, intriguing mixed-valence chemistry, and versatile catalytic properties [5-7]. 

Scheme 8.2. Synthetic access to base-free cationic zirconocenes.

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