Sodium unsubstituted derivatives

Sodium borohydride and 3-isoxazolium salts with a 3-unsubstituted position also give isoxazolines, as do the 3-substituted 5-unsubstituted derivatives. With the latter group, further reduction occurs to the isoxazolidines (74CPB70). 

A special rearrangement in the 1,2,4-thiadiazole series concerns the 2-phenylamino-l,2,4-thiadiazolo [2,3,-a]pyridinium salts (275 R = H, Me), which are obtained by oxidation of N-(2-pyridyl)thioureas (Scheme 45). In the case of the unsubstituted derivative (275 R = H X = Br), neutralization with sodium acetate in ethanol produces directly benzothiazole 277... 

Tetrahydro-4//-pyrido[l,2-a]pyrimidin-4-one was prepared by the decarboxylation of 6,7,8,9-tetrahydro-4-oxo-47/-pyrido[ 1,2-a]pyrimi-dine-3-carboxylic acid in 85% phosphoric acid at 160-170°C for 6 hours (85ACH305). Decarboxylation of 9-anilino-4-oxotetrahydropyridopy-rimidine-3-carboxylic acid derivatives 422 occurred in refluxing 2% aqueous sodium hydroxide under argon to give 3-unsubstituted derivatives 423 [85JCS(P1)1015],... 

The unsubstituted l,3-dithiole-2-thione (245) can be accessed, however, by the reaction of dimethyl acetylenedicarboxylate with l,3-dithiolane-2-thione (Scheme 50) <74JOC2456>, from the reaction of sodium acetylide with carbon disulfide and elemental sulfur <64CB1298>, or by a two-step synthesis from the 1,2-dichloroethyl ethylether (246) and potassium trithiocarbonate. The intermediary 4-ethoxy-l,3-dithiolone-2-thione (247) affords, upon reaction with p-toluene sulfonic acid with concomitant loss of ethanol, the unsubstituted derivative (245) <76CC920>. 

From the dimethyl acetal derivatives of perhydropyrido[l,2-c][l,3]oxa-zines (33 and 34), the phenylsulfonyl group was reductively removed with sodium amalgam to yield 5-unsubstituted derivatives (96SL100). 

The A-ring of the 17-ol (25) derived from equilenin 3-methyl ether is reduced rapidly under Birch reduction conditions, since the 1,4-positions are unsubstituted. The B-ring is reduced at a much slower rate, as is characteristic of aromatic compounds in which 1,4-reduction can occur only if a proton enters an alkylated position. Treatment of (25) with sodium and t-butyl alcohol in ammonia reduces only the A-ring to afford the corresponding 1,4-dihydro compound in over 85% yield.On the other hand,... 

For unsubstitUted or lower alkylated dioxotriazines, it is advantageous to cyclize semicarbazones by sodium ethylate in ethylene glycol as described by Chang and XJlbricht. In this reaction 6-aza-uracil is obtained in 66% yield. The procedure was used for the preparation of labeled 6-azauracil ° and later for the synthesis of a number of 6-alkyl derivatives including 6-azathymine. °... 

Of greater versatility is an extension of Albert and Royer s acridine synthesis. The first successful use of this in the quinazoline series was for the removal of the chlorine atom in 2-chloro-4-phenylquin-azoline, although it had been used previously to prepare 8-nitro-6-methoxyquinazoline in very poor yield. The 4-chloroquinazoline is converted to its 4-(A -toluene-p-sulfonylhydrazino) quinazoline hydrochloride derivative which is decomposed with alkali in aqueous ethylene glycol at lOO C (Scheme 13). The yields are high (60-70%) when R is Me, Cl, OMe but low when R is NO2, and in the latter case it is preferable to use dilute sodium carbonate as the base. This reaction is unsatisfactory if the unsubstituted pyrimidine ring is unstable towards alkali, as in 1,3,8-triazanaphthalene where the pyrimi-... 

Unsubstituted or alkyl-substituted 2-alkenyllithium, -sodium and -potassium derivatives are of little value in stereoselective carbonyl addition reactions. In general, these reagents exhibit high... 

Treatment of dibromides 2 with sodium azide in N,N-dimethylformamide (DMF) at room temperature resulted in the formation of two products, 3-(a-azidobenzyOchromones 2a-c,g or -1-thiochromones 2d-f and the 3-arylidenechromanones la-c,g,h or -1-thiochromanones Id-f, respectively (eqn. 2). As shown by yield data given in Table 2, the substituent at position 2 plays decisive role in the product ratio. Dibromides unsubstituted at position 2 tended to give almost exclusively azides 3a-f and only a small amount of 1 was obtained. On the contrary, the reaction of flavanone derivatives 2gjh gave 3-arylideneflavanones... 

The success of this reaction was ascribed to the solubility of the chlorozinc intermediate, whereas other chloramine-T derivatives (e.g. the sodium salt) are insoluble. An alternative non-nitrene pathway was not eliminated from consideration. On the other hand, no aromatic substitution or addition, characteristic of a free sulphonyl nitrene (see below), took place on treatment of jV,lV-dichloromethanesulphonamides with zinc powder in benzene in the cold or on heating. The only product isolated was that of hydrogen-abstraction, methanesulphonamide 42>, which appears to be more characteristic of the behaviour of a sulphonyl nitrene-metal complex 36,37). Photolysis of iV.iV-dichloromethanesulphonamide, or dichloramine-B, or dichloramine-T in benzene solution led to the formation of some unsubstituted sulphonamide and some chlorobenzene but no product of addition of a nitrene to benzene 19>. 

Substitution at the 9-position was well tolerated, but some long-chain lipophilic substituents or acyl groups reduced activity. Alkylation or acylation of the unsubstituted compound in the presence of sodium hydride afforded derivatives substituted on the indole nitrogen atom (Table 7.4). 

The 2-aminoquinazolines 259 were prepared in two independent ways. The 2-quinazolinone 258 was transformed to 2-aminoquinazoline 259 by treatment with phosphorus oxychloride and subsequently with sodium amide in liquid ammonia, or with phosphorus pentachloride under carefully controlled conditions [75JCS(P1)1471]. Attempts to prepare the N-substituted derivatives failed, but the reaction was successful with the unsubstituted cis cyclopentane-fused homolog [76JCS(P1)1415]. 

The A -unsubstituted 5-dimethylamino-l,2,4,3-triazaphosphole is converted to its anion by sodium, potassium, or their hydrides (80ZN(B)1222>. Boryl (86PS(28)7I>, silyl (80ZN(B)1222>, stannyl, phosphino, and (thio)phosphinyl <80ZN(B)1222> derivatives have been prepared mostly by reaction of the triazaphosphole with the corresponding chloride the substituents become attached to N-2. 

The authors of this review have developed a straightforward procedure for the synthesis of unsubstituted and alkyl-substituted thieno-thiophenes 1, 2, and 3 the method involves intramolecular condensation of ortho-bifunctional thiophene derivatives. Vilsmeier formylation of an alkyl (5-ethyl-2-thienylthio)acetate (53) furnishes the (5-ethyl-3-formyl-. 2-thienylthio)acetate (54) which when heated with alcoholic sodium... 

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