Synthesis chlorite

Some interesting organic chemistry is involved in the synthesis of chlorite-resistant brighteners for acrylic fibres. None of these compounds is easy to make and methods for preparation of the starting materials can be complex. Much manufacturing know-how is involved. One route for introduction of the benzimidazole nucleus into structure 11.55 is shown in Scheme 11.22. Preparation of the chemically rather simpler benzoxazole grouping in product 11.56 is shown in Scheme 11.23. 

In the synthesis procedure for chlorine(IV) oxide in Volume IV, page 153, the required approximate amount of sodium chlorite should be 0.13 g. instead of 1.3 g. 

This methodology provides a general synthesis of L-amino acids in 92-96% ee and in chemical yields of about 40-60%. Thus reaction of 3 (X = Br) with NaN3 under phase-transfer conditions provides 6, which is homologated to the 1-chloro-2-azidoboronate 7. This product is oxidized by sodium chlorite directly to an azido carboxylic acid (8). Hydrogenation of 8 provides L-amino acids (9). 

For the synthesis of amino acids, the reaction of an a-haloalkyl boronic ester 4 with sodium azide and a phase-transfer catalyst in dichloromethane/water requires a large excess of azide in order to form the a-azidoalkyl boronic ester 5 with only 1-2% epimer34. With the exception of R1 = benzyl, where epimerization of 4 is relatively rapid, bromoalkyl boronic esters are preferred. Chloroalkyl boronic esters react so slowly that the azide and dichloromethane may generate hazardously explosive diazidomethane65,66. Chain extension of 5 to 6 proceeds normally. Sodium chlorite, which is known to oxidize aldehydes to carboxylic acids67-69, also oxidizes a-chloroalkyl boronic esters to carboxylic acids34. The azido acid is hydrogenated to the amino acid. 

The Sharpless asymmetric dihydroxylation has played a prominent role in enantioselecitve organic synthesis. Two groups have recently reported improvements in the procedure. Osmo E.O. Horni of the University of Oulu, Finland has found (J. Org. Chem. 2004,69,4816) that sodium chlorite is a more efficient reoxidant than is the usual K,[Fe(CN)J. Carlos A.M. Alfonso of the Instituto Superior , Lisbon has reported (J. Org. Chem. 2004,69,4381) that the asymmetric dihydroxylation can... 

Microprobe analyses of some berthierine pellets from sedimentary rocks (Velde, e t al., 1974, and new data, Figure 30) indicate that these minerals have compositions close to those of 7 8 chlorites delimited by synthesis studies and here there is a more restricted range of silica substitution in the structure than is found in 14 8 chlorites. Thus the two polymorphs have at least different limits in tetrahedral substitutions. 

Caillere, S., 1954. Synthesis de quelques phyllites nickeliferes. Compt. Rend., 239 1535- 1536. Caillere, S., 1962. A new type of chlorite. Bull. Groupe Franc. Argils., 13 35-37. 

Nelson, B.W. and Roy, R., 1958. Synthesis of the chlorites and their structural and chemical constitution. Aitt Mineralogist, 43 707-725. 

The closing stages of Carreira s synthesis of (+ )-zaragozic acid C (Scheme 7.4) began with the Dess-Martin oxidation6 of 18. An ozon-olysis next yielded trialdehyde 19, and a buffered sodium chlorite oxidation provided the corresponding triacid. Of particular interest here was... 

An excellent example where a capsid virus has been given a new supramolecular application can be found in the work of Nolte who took an icosahedral capsid virus, cowpea chloritic mottle virus (CCMV) and used it as a nanoreactor for polymer synthesis [30], Natural CCMV spontaneously assembles in acidic aqueous solution and disassembles in basic solution. The capsid contains pores open at pH 5 to release RNA into the host. Once the RNA leaves, the empty capsule is left. The Nolte group was able to assemble the subunits around polystyrene sulfonate with a mass of 9.9 kDa but the resulting structure had a different morphology to the natural system. Indeed, capsules formed around polymers with masses between 2 and 85 kDa but not around those with masses above 100 kDa. This raised the question of the potential for polymers to form within a capsid but to test the possibility a mixture of botanical, biological and chemical approaches was needed. 

A further oxidation is then performed to establish the carboxylic acid moiety at C-1, which will form the macrolactone later in the synthesis. Sodium chlorite is commonly used as an oxidizing agent and is often applied for saturated and aromatic aldehydes. Hypochloric acid (HOCl) and sodium hypochlorite (NaOCl) are formed as byproducts and have to be destroyed before they can attack the substrate or the product, because they are stronger oxidizing agents. In this case, 2-methyl-2-butene (43) is added to the reaction mixture forming a chlorohydrin 44. 

In the final stages of the total synthesis of ustiloxin D, M.M. Joullie and co-workers had to install the amide side-chain onto the already assembled macrocycle.To achieve this goal, the macrocyclic primary alcohol was treated with the Dess-Martin periodinane to generate the corresponding aldehyde, which was subsequently treated with sodium chlorite to afford the carboxylic acid. The carboxylic acid was then coupled with the benzyl ester of glycine to complete the installation of the side-chain in 66% yield for three steps. 

Alkoxy-3-chloro-3//-diazirines are obtained by the chlorination (aqueous sodium hypo-chlorite/dimethyl sulfoxide) of the corresponding amidines. They serve as precursors for the synthesis of 3-fluoro derivatives via the reaction with anhydrous tetrabutylammonium fluoride (for an improved procedure for the dehydration of commercial tetrabutylammonium fluoride trihydrate, see ref 26). This is a much simpler method than the earlier described preparation of 3-fluoro-3-methoxy-37/-diazirine involving the elemental fluorination reaction and a shatteringly explosive fluoronitrogen intermediate. 

Use of polymer-bound chlorite 11 was shown to be more efficient for the oxidation of secondary alcohols to the corresponding ketone [23c]. The method was applied to a series of complex synthetic intermediates and gave excellent results. Immobilized chlorite was shown to be also a very efficient co-oxidant in the conversion of primary alcohols into the corresponding carboxylic acid [24]. This method is particularly attractive due to the ease of purification, the excellent yields and purity obtained also on more complex structures. What makes these techniques particularly interesting is that they have found applications in the synthesis of complex molecules. It was the method of choice for the synthesis of intermediate 13, the core of azadirachtin, in studies towards the synthesis of this natural product by the Nicolaou group [25]. This bicyclic aldehyde was obtained very cleanly using this method (Scheme 4.2). 

New Cooxidants for Dihydroxylation. In recent studies, several oxidants, 02, air, NaC102 (sodium chlorite), NaOCl (sodium hypochlorite), PhSe(0)Bn, Ba(C10)3, and Me3NO 8- were successfully used as cooxidants in Os-catalyzed dihydroxylation of olefins. For instance, Donohoe reported on the use of Me3N0 as a cooxidant in the dihydroxylation process, which allows the synthesis of ( )-l-epiaustraline in 14% overall yield from iV-Boc-p3Trole 2,5-methyl diester (eq 47). The construction of syn-diol moiety is employed by means of 0s04-Ba(C10)3 oxidation (eq 48). ... 

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