1.3- Oxazines basicity

A number of simple reactions are now known which form 2-oxo-tetrahydro-1,3-oxazine (18). Here, also, 3-aminopropanol and some of its derivatives are frequently used, Cyclizing reagents are carbonic acid esters in strongly basic medium, " ethyl chloropropionate, trichloracetic esters, or phenyl isocyanate. An example of the first of these methods is ... 

In a basic medium, 5-nitro-5-hydroxymethyltetrahydro-l,3-oxazine derivatives can be coupled with aryl diazonium salts to form aryl-azo derivatives (54) with the elimination of a molecule of formaldehyde. ... 

Dihydro-2/7- 74 and -4//-l,2-oxazines and thiazines 75 are interrelated by prototropy, being enamines and imines, respectively. In the case of oxazines, the imine form 75 is favored, and there are several well established examples of this system, including the parent heterocycle 75 (X = O) [84MI2]. No tautomeric equilibrium between the 2H and 4H forms has been observed under normal conditions in solution or in the solid state. However, the formation of intermediate 2H isomers 77 was proposed both for the conversion of 3-phenyl-5,6-dihydro-4//-l,2-oxazine 76 (R = Ph, r = R = H) into 2-phenylpyrrole(89TL3471) under strong basic conditions and for thermal decomposition of cyclopentene-fused 1,2-oxazine 76... 

An analogous isomerization to the intermediate 79 was reported to occur upon the basic cleavage of oxazine A-oxides 78 (88BCJ461). 

Motpholines are a chemical class of organic compounds with the six-membered ring tetrahydro-1,4-oxazine, as their basic structure. 

Benzoyl leuco Basic Blue 3 (2) is a typical cyan leuco oxazine used in carbonless copy paper. To satisfy the requirements of new applications such as electrolytic recording and Color Dry Silver, new oxazine leucos have been... 

A new synthetic route for functionalized polyhydroxyalkyl-pyrimidines starting from unprotected aldoses and based on montmorillonite K-10 catalysis and solvent-free microwave irradiation conditions, has been reported by Yadav et al,m Thus, reaction of D-glucose and D-xylose with semicarbazide or thiosemicarbazide (186) in the presence of montmorillonite K-10, under microwave irradiation, proceeded via domino cycloisomerization, dehydrazination, and dehydration of the intermediate semi- or thiosemicarbazones (187) to afford l,3-oxazin-2-ones or l,3-oxazine-2-thiones (188) in one single step and in yields between 79% and 85% (Scheme 34). Other mineral catalysts tested, such as silica gel and basic alumina, were far less effective for this transformation and only silica gel was active at all, giving low yields (15-28%) of compounds 188a-d. The l,3-oxazin-2-ones(thiones) thus synthesized were subsequently converted into the target pyrimidines by reaction with aromatic... 

Many brilliantly coloured and tinctorially strong basic dyes for silk and tannin-mordanted cotton were developed in the early decades of the synthetic dye industry. Most of these belonged to the acridine, azine, oxazine, triarylmethane, xanthene and related chemical classes their molecules are usually characterised by one delocalised positive charge. Thus in crystal violet (1.29) the cationic charge is shared between the three equivalent methylated p-amino nitrogen atoms. A few of these traditional basic dyes are still of some interest in the dyeing of acrylic fibres, notably as components of cheap mixture navies and blacks, but many modified basic dyes were introduced from the 1950s onwards for acrylic and modacrylic fibres, as well as for basic-dyeable variants of nylon and polyester [44] ... 

Bindschedler s Green (6.204) can be made by condensing p-nitroso-N,N-dimethylaniline with N,N- dimethyl aniline. A similar condensation with 2-naphthol gives Meldola s Blue (6.209 Cl Basic Blue 6), the first oxazine dye, discovered in 1879. The symmetrical Cl Basic Blue 3 (6.210) is of more commercial significance. It is synthesised by nitrosation of N,N-diethybrn-anisidine followed by condensation with N,N-diethybm-aminophenol, and is used for dyeing acrylic fibres. This dye is now classified by ETAD as toxic [73]. 

Synthesis of a C(8)-C(18) segment of the larger fragment of lb using the same basic strategy is depicted in Scheme 25. Here, hydroxy ketone 176 was subjected to syn-selective (dr of crude product=90 10) reductive amination [42] with sodium cyanoborohydride and benzylamine followed by tetrahydro-oxazine formation using aqueous formaldehyde. The resulting heterocycle 182 was then converted to unsaturated ester 184 by successive desilylation, oxidation, and entirely (Z)-selective Horner-Wadsworth-Emmons olefination. Re-... 

A basically new type of synthesis of dihydrooxazines was applied for the preparation of 177 and 179 (86JOC3248). Boron trifluoride catalyzed the intramolecular [4+2] cycloaddition of the A-acyliminium compounds derived from 176 and 178, resulting stereospecifically in the rrani-fused cyclo-pent[d][l,3]oxazines and partly saturated 3,1-benzoxazines 177 and 179, respectively. The steric orientation of the 4-methyl substituent of the product is controlled by the Z and geometry of the starting bisamides 176 and 178 (86JOC3248). 

The delocalised charged dyes are dominated by cyanine dyes, exemplified by the azacarbocyanine Cl Basic Yellow 11 (2.27), the diazacarbocyanine Cl Basic Yellow 28 (2.30) and the diazahemicyanine Cl Basic Blue 41 (2.49). Where necessary quatemisation is carried out as a post colour forming reaction. Other structural types include oxazines, thiazines and triphenyhnethane dyes. 

The preparation of oxazolines from p-hydroxy amides and SOCI2 via the corresponding p-chloro amides under basic conditions is well known and has been discussed earlier. Potassium fluoride on alumina has been reported as a mild alternative to the aqueous or alcoholic bases that are commonly used. The reaction is typically carried out in acetonitrile or tetramethylene sulfone and moderate to good yields of oxazolines and oxazines can be obtained as shown in Scheme 8.29. 

The tetrahydro compounds are strongly basic and may be jV-alkylated directly with alkyl halides (64T1173). A number of N-nitroso derivatives have been made by the oxidation of tetrahydro- 1,3-oxazines with peracids (74T3315). Sequential treatment of the oxazine (77) firstly with diketene and then with 4-methyIbenzenesulphonyl azide and triethylamine gives the diazoketone (78), which on irradiation with UV light yields the cepham (79) exclusively (79CC846). 

Another widely used approach is the cyclization of oximes either under acidic, as in the conversion (147 ->148) (71MI22700), or basic conditions (149- 150) (78JOC2020). Cyclopropyl ketones (151) also react with hydroxylamine hydrochloride to give dihydro-1,2-oxazines (153), probably via the protonated oxime (152). If this is so then this reaction represents a rare example of a 6-endo-tet ring closure <80AG(E)199). 

These and other venerable synthetic routes to the tricyclic oxazines and thiazines have been reviewed in detail (B-78MI22701). 2-Hydroxy(or mercapto)-2, 4 -dinitrodiphenylamines readily cyclize to phenoxazines (or phenothiazines) in basic media through elimination of nitrous acid. This is the so-called Turpin reaction, which is complicated by the fact that the intermediate Meisenheimer complexes (251) may undergo a Smiles-type rearrangement so that mixtures of isomeric products are obtained (Scheme 112). 

The same authors have also reported that the (E)- and (Z)-4-alkylidene-(3-lactams have shown a different reactivity in the acylation reactions under basic conditions [278]. For instance, the E isomer formed readily the ALacyl-4-alkylidene-(3-lactam, while the Z isomer reacted sluggishly rearranging to the corresponding oxazin-6-one (I and II, respectively, Fig. 15). 

Deprotection of the N-Boc group of piperidine 305 by TFA to afforded a TFA salt, followed by basic aqueous workup with aqueous NaHC03 solution gave a single racemate of perhydropyrido[2,l-c][l,4]oxazin-3-one 306, while that of the O-TBS protected piperidine 307 by TFA or TBAF yielded diastereomeric mixtures of 308 (09OBC655). 

Basic (cationic) dyes contain cationic groups which are ionized in the dyebath. They are applied to acrylics, nylon, polyester, and paper and are most often azo, anthraquinone, triarylmethane, quinoline, thiazine, methine, oxazine, and acridine types. 

Oxazine, azine and thiazine dyes are named for the characteristic heterocyclic ring systems 1,4-oxazine, 1,4-diazine, and 1,4-thiazine. The dyes are generally cationic (basic) or acid dyes. They also can be reduced to colorless forms, then oxidized back to the dye, as in vat dyeing. The dyes also have been used to a limited extent in disperse and fiber reactive applications. They are used as titration indicators and may be applied to acrylic fibers and leather. 

Basic paper, polyacrylonitrile, modified nylon, polyester and inks applied from acidic dyebaths cyanine, hemicyanine, diazahemi-cyanine, diphenylmethane, triaryl-methane, azo, azine, xanthene, acridine, oxazine, and anthraquinone... 

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