Thio-analogues

C-nmr data have been recorded and assigned for a great number of hydantoin derivatives (24). As in the case of H-nmr, useful correlations between chemical shifts and electronic parameters have been found. For example, Hammett constants of substituents in the aromatic portion of the molecule correlate weU to chemical shifts of C-5 and C-a in 5-arylmethylenehydantoins (23). Comparison between C-nmr spectra of hydantoins and those of their conjugate bases has been used for the calculation of their piC values (12,25). N-nmr spectra of hydantoins and their thio analogues have been studied (26). The N -nmr chemical shifts show a linear correlation with the frequencies of the N—H stretching vibrations in the infrared spectra. 

The pyrano[2,3-[Pg.123]

Probably the best synthesis of 5-methylcytosine is via its 2-thio analogue (964 X = S) (49JBC(177)357) but the following briefly-described route may be preferable 2,4-dimethoxy-5-methylpyrimidine (965) with acetyl chloride gives the 1-acetyl derivative (966) which on aminolysis in aqueous ammonia gives 5-methylcytosine (964 X = O) in good overall yield (68TL2171). 

These include copolymers of propylene sulphide with 3-10% of allyl glycidyl thioether and which may be considered as a thio-analogue of the propylene oxide-allyl glycidyl ether rubber briefly mentioned in Section 19.5 ... 

Sinee sulphur is in the same group as oxygen in the periodie table it replaees oxygen in organie stmetures to produee thio analogues sueh as ... 

By contrast to the plethora of simple oxo-halides and thiohalides of P, the corresponding derivatives of P are fugitive species that require matrix isolation techniques for preparation and characterization ClPO, BrPO, FPS and BrPS all form non-linear triatomic molecules, as expected. The corresponding oxosulfide, BrP(0)S, and its thio-analogue, FP(S)S, have also recently been isolated. 

Numerous charged sulfur-nitrogen species have been synthesized in recent years, particularly those having an odd number of N atoms which would otherwise be paramagnetic. However, thio analogues of nitrites (N02, p. 461) and nitrates (N03, p. 465) are unknown. 

Thiazolotriazines 678 were synthesized (87AJC693) by heating 5-acyl-amino[l,2,4]triazin-6(lH)-ones or its thio analogue 677 with phosphorus... 

Carb-29. Hemiacetals and hemithioacetals 2-Carb-30. Acetals, ketals and their thio analogues 2-Carb-31. Names for monosaccharide residues... 

Carb-29. Hemiacetals, hemiketals and their thio analogues... 

Treatment of a chiral amine with phosgene is the cheapest way to prepare symmetrical ureas [29]. Nevertheless, due to the toxicity and reactivity of that reagent, it can advantageously be replaced by triphosgene [30] or l,l -carbonyldiimidazole [31-34] or other derivatives such as l,l -carbonyldi-2(lH)-pyridinone [35]. This procedure can be extended to thiophosgene (Scheme 1) and its thio-analogues, such as l,l -thiocarbonyldi-2(lH)-pyridinone to produce thioureas [36] chiral diamines can thus be transformed into the corresponding monoureas or monothioureas. 

Nucleophilic attack of amines on fully esterified derivatives of phosphoric acid and its thio-analogues may in general occur at phosphorus or carbon. In an attempt to correlate the rates with structural factors, a study has been reported on a series of compounds of the type (49), ... 

The colored form of 2,2-diphenyl-2//-thiochromene (thio analogue of chromene) absorbs at 650 nm in 3-methylpentane at 77 K.71... 

Becker and Kolc first examined the photochromism of spiroindo-linobenzothiopyran 44, a thio analogue of spiroindolinobenzopyran (Scheme 19). The closed form of this spirobenzothiopyran is stable and the photocoloration is very slow, compared with spiropyrans.71... 

Modro has synthesized a series of phosphoric triamides from P(0)C13 as outlined in Scheme 33 <2001PJC1089>. This approach was not successful in forming the thio analogue but direct condensation of P(S)C13 with the triamine 322 yielded the thiophosphoryl analogue compound 323 (Scheme 34). 

A more complex cycloaddition type is observed when diphenyl cyclopropenone and its thio analogue are reacted with the pyrylium betaine 451276 and the products obtained were assigned structures 450 and 452, respectively. 

Other conversions of hydroxyl-substituted compounds (or their lactam tautomers), their thio analogues, as well as amines are listed in Table 8. These reactions involve 0-, N-, or -alkylations or acylations, O-S exchange reactions, or other analoguous processes. 

Also 2-alkylpyridazinones of type (4, R1, R2 = alkyl) [26, 27] and type (5, R1, R2 = alkyl) [28, 29], being regioisomers of compounds (2), as well as thio-analogues (6, R1, R2 = alkyl) [30] and 2-alkenyl congeners [31], have been reported in the patent literature to exhibit such activities. Structure-activity... 

The most potent among the compounds tested were the pyridazi-nones (28, R1 = Ph, R2, R3, R4, R5 = H, n = 2-5) [101]. Structure-activity relationships have been investigated in detail with this type of compound. Also, thio-analogues of compounds (28) (3-pyridazinethione derivatives) as well as 2-aminoalky]-6-aryl-3(2//)-pyridazinones were claimed in patents as gastric secretion inhibitors or anti-ulcer agents [100, 102, 103]. 

Table A5.12 Cleavage of p-nitrophenyl acetate and its thio analogue by cyclodex-trins."...

Ketenylidenetriphenylphosphorane and its thio-analogue (2) can be obtained from the corresponding ester ylides by treatment with sodium bis(trimethylsilyl)-amide (4).7 Salt-free solutions of alkylidenetriphenylphosphoranes can be conveni-... 

Alkyl and aryl arenediazoates ( diazoethers ) are generally unstable and even explosive compounds. They are produced by interaction of alcohols with (explosive) bis(arenediazo) oxides, or of -blocked phenols with diazonium salts. The thio analogues are similar. Individually indexed compounds are ... 

The thio analogue behaves similarly, whereas the propargylic derivative is converted into the corresponding stable vinylic telluride. 

A structurally related 2-thio analogue, 4-amino-5-methyl-2-thiouracil (LVII) possesses growth inhibition against L. leichmannii. This inhibition could be reversed in a non-competitive manner by vitamin B12 [408]. 

The extraordinary activation of the 5-CI3C group is further demonstrated by comparison of (68) with the thio analogues (69). The whole CI3C group of (68) is displaced by piperidine (Equation (15a)) <73CPB1641>, while under similar conditions only one chlorine atom is displaced in the thiadiazoles (69) (Equation (15b)) <86PS(26)151>. 

Other useful nucleophiles for this type of substitution include azide and thiolacetic acid. Glaxo researchers utilized such a strategy in their synthesis of the neuraminic acid analogue 346 (Scheme 8.109). ° Itzstein and co-workers used a similar strategy to synthesize a thio analogue of neuraminic acid 347 °" and reported that thiolacetic acid was also a suitable nucleophile. ° ... 

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