Cyanates functional derivatives

The results show that the dediazoniations afforded dihydrofuran derivatives which were functionalized exclusively at the site of the cyclized radical (10.58, Z = 0, n = 1) in very good yields for bromination and iodination, and moderate yields for chlorination, phenylthionation, and cyanation. All cyclizations take place in the exo mode, i.e., at the -CH= (second-last) carbon and not at the CH2 group (endo mode for nomenclature see Beckwith et al., 1980). 

The corresponding /i-amino aldehydes are reduced in situ and the corresponding amino alcohols are isolated in good yield with up to >99 % ee. The Mannich reactions proceed with excellent chemoselectivity and inline formation occurs with the acceptor aldehyde at a faster rate than C-C bond-formation. Moreover, the one-pot three-component direct asymmetric cross-Mannich reaction enables aliphatic aldehydes to serve as acceptors. The absolute stereochemistry of the reaction was determined by synthesis and reveled that L-proline provides syn /i-amino aldehydes with (S) stereochemistry of the amino group. In addition, the proline-catalyzed direct asymmetric Mannich-type reaction has been connected to one-pot tandem cyanation and allylation reaction in THF and aqueous media affording functional a-amino acid derivatives [39, 42]. 

In the above-mentioned patents post-polymerization modification is performed in a single step. An alternative is the performance of two sequential modification steps. In the first step the polymer is reacted with tin or germanium derivatives (triphenyl tin, tributyl tin, diphenyl tin dichloride, dioctyl tin dichloride, phenyl tin trichlorde etc.). In the subsequent modification step heterocumulene compounds (ketenes, thioketenes, isocyanates, thioiso-cyanates and carbodiimides) are applied [437,438]. Specific interaction with silica is obtained by end group functionalization with vinyl monomers which contain hydroxyl or epoxy groups. The effects are observed if the PDI is below 5 [439,440]. 

The present volume, Supplement D2 retains the title of its direct predecessor, Supplement D The chemistry of halides, pseudo-halides and azides, even though it deals only with derivatives of fluorine, chlorine, bromine, iodine and astatine. Hence, in order to keep the Chemistry of the functional groups series complete and up-to-date, it will be necessary to publish, in the not too distant future, an additional supplementary volume ( D3 ) discussing the recent advances in the chemistry of azides, cyanates, isocyanates and their thio derivatives. 

Patai, S. (Ed.) The Chemistry of Functional Groups. The Chemistry of Cyanates and their Thio Derivatives, Wiley-Interscience New York, 1977. 

The reaction of proteins with cyanate has been exploited in the development of a method for the quantitative determination of NH2-terminal residues (Stark 1967a), as well as in a variety of interesting structure-function studies exemplified by those of Smyth (1967) on oxytocin, and Cerami and Manning (1971), as well as Lee and Manning (1973), on sickle cell hemoglobin. Whereas cyanate reacts with a-NH2, -NH2, thiol, imidazole, and phenolic OH groups of proteins, only the amino group derivatives are stable at alkaline pH. 

Substituted 2-oxazolidones 165 are useful chiral auxiliaries for diastereoselective functionalization at the a-carbon of their amide carbonyl group. The a-fluoroaldehydes 166 were prepared by a series of reactions electrophilic fluorination of the corresponding oxazolidinone sodium enolates with AMluorobenzenesulfonimine reductive removal of the auxiliary with LiBH4 and Dess-Martin oxidation. The aldehydes are so unstable for isolation that they are converted with (R)-/ -toluenesulfinamide to /7-toluenesul(inimines 167, which are isol-able and satisfactorily enantio-enriched. Chiral sulfinimine-mediated diastereoselective Strecker cyanation with aluminum cyanide provided cyanides 168 in excellent diastereose-lectivity, which were finally derived to 3-fluoroamino acids 169 (see Scheme 9.37) [63]. 

A variety of CEs with tailorable physico-chemical and thermo-mechanical properties have been synthesized by appropriate selection of the precursor phenol [39,40]. The physical characteristics like melting point and processing window, dielectric characteristics, environmental stability, and thermo-mechanical characteristics largely depend on the backbone structure. Several cyanate ester systems bearing elements such as P, S, F, Br, etc. have been reported [39-41,45-47]. Mainly three approaches can be seen. While dicyanate esters are based on simple diphenols, cyanate telechelics are derived from phenol telechelic polymers whose basic properties are dictated by the backbone structure. The terminal cyanate groups serve as crosslinking sites. The polycyanate esters are obtained by cyanation of polyhydric polymers which, in turn, are synthesized by suitable synthesis protocols. Thus, in addition to the bisphenol-based CEs, other types like cyanate esters of novolacs [37,48], polystyrene [49], resorcinol [36], tert-butyl, and cyano substituted phenols [50], poly cyanate esters with hydrophobic cycloaliphatic backbone [51], and allyl-functionalized cyanate esters [52] have been reported. 

K. Wittel, J. K. Meeks and S. P. McGlynn, in The Chemistry of Functional Groups Cyanates and their Thio Derivatives (Ed. S. Patai), Vol. 1, Wiley-Interscience, Chichester, 1977, p. 1. 

Coordinated cyanamide does not add OH" to form the N-bound urea complex since it de-protonates 5.2) to ve the unreactive [Co(NCNH)(NH3)5p ion, but in acid it readily loses NH to form N-coordinated cyanate (equation 27). The analogous dimethylcyanamide complex cannot deprotonate and adds OH" to form urea (Scheme 21), but this does not proceed further to coordinated carbamic add and NHMCj in a process analogous to that suggested for the function of Ni in the metalloenzyme jack bean urease (which catalyzes the convemioo of urea to these products), nor does it lose NHMc2 to form the cyanato complex as suggested by Balahura and Jordan for the similar urea derivatives (equation 28). Alternatively, in acid solution the protonated urea rapidly isomerizes to the O-coordinated complex (r,/2 a 40 s, 25 °C Scheme 21). This isomer undergoes OH -catalyzed hydrolysis at the metal rather than at acyl carbon, so the function of the metalloenzyme has not been duplicated in this system. A similar property is found for 0-bound urea (equation 29). ... 

Rh-catalyzed direct C-H cyanation of aryl oximes with the cyano transfer group JV-cyano-A/ -phenyl-/)-toluenesulfonamide has tilso been reported [84]. This was the first report of a Rh-catalyzed-directed C-H cyanation reaction for the synthesis of aromatic nitriles. JV-Cyano-JV-phenyl-/)-toluenesulfonamide, a user-friendly cyanation reagent, was used in the transformation. Many different directing groups can be used in this C-H cyanation process, and the reaction tolerates a variety of synthetically important functional groups. This methodology was nicely used for the synthesis of the cyanated derivative of the nonsteroidal anti-inflammatory drug zaltoprofen in a yield of 74% (Scheme 4.12). 

Cyanation. The addition of nitrile functionalities to molecules is a viable route for the introduction of carbonyl derivatives. An example of this approach can be seen in the Lewis base-catalyzed cyanomethylation of benzaldehyde with (trimethylsilyl)propio-nitrile. The Lewis base catalyst activates the Si-C bond of (trimethylsilyl)propionitrile, allowing the subsequent attack at the target aldehyde center, providing the substituted benzylic alcohol in good to excellent yields. However, upon treatment of the same starting materials with both Lewis base catalyst and TBAT, overall yields declined (eq 20). 

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