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Technological advancements in optoelectronic motion capture systems have allowed for the development of high-precision computer-assisted surgery (CAS) used in cranial and spinal surgical procedures. Errors generated sequentially throughout the chain of components of CAS may have cumulative effect on the accuracy of implant and instrumentation placement - potentially affecting patient outcomes. Navigational integrity and maintenance of fidelity of optoelectronic data is the cornerstone of CAS. Error reporting measures vary between studies. Understanding error generation, mechanisms of propagation, and how they relate to workflow can assist clinicians in error mitigation and improve accuracy during navigation in neurosurgical procedures. Diligence in planning, fiducial positioning, system registration, and intra-operative workflow have the potential to improve accuracy and decrease disparity between planned and final instrumentation and implant position. This study reviews the potential errors associated with each step in computer-assisted surgery and provides a basis for disparity in intrinsic accuracy versus achieved accuracy in the clinical operative environment.

On thermolysis of 4-methoxy- and 4-alkylamino-2-(2-chloroethoxy)-6-morpholino(piperidino)-sym-triazines, the corresponding oxazolo- or imidazo-sym-triazinones are formed by elimination of methyl chloride or hydrogen chloride, and 4,6-disubstituted 3-(2-chloroethyl)-sym-triazin-2-ones are formed from 4,6-dimorpholino(dipiperidino) derivatives.

2-Dimethylamino-4,6,7,8-tetrahydroimidazo[1,2-a]-sym-triazin-4-one synthesized by us previously is converted by the action of aryl isocyanates and arenesulfonyl chlorides into the corresponding derivatives of urea and N-arenesulfonyl-substituted imidazo-sym-triazinones. It was shown that 6-(2-chloroethoxy)-2-dimethylamino-4-(methoxycarbonylmethylamino)-sym-triazine is converted by thermolysis into 2-dimethylamino-8-methoxycarbonylmethyl-4,6,7,8-tetrahydroimidazo[1,2-a]-1,3,5-triazin-4-one, which is also obtained by the action of methyl bromoacetate on the imidazo-sym-triazinone.

Treatment of 3,4-dimethyl-2-thioxothiazoline-5-carboxylic acid hydrazide with NH4SCN and PhCONCS gave the corresponding thiosemicarbazides, arylsulfochlorides yielded the arylsulfonylhydrazides, and diazotization conditions gave the corresponding azide. The interactions of the latter with different nucleophiles have been studied and a series of novel carbamic acid, urea, and semicarbazide derivatives containing a thiazoline fragment have been prepared.

We have used 1H NMR to study the amine-imine tautomerism of some esters and amides of 2-N-labeled 4-methylthiazole-5-carboxylic acids and 5-carbamic acids. We have shown that the nature of the substituents of the 2-NHR1, 5-COR2, or 5-NHCOR2 groups affects that position of the tautomeric equilibrium.

Acylation of the ethyl ester and anilide of 2-amino-4-methylthiazole-5-carboxylic acid gave 2-acetyl(arylsulfonyl)amino derivatives. Methylation of acetylaminothiazole and subsequent deacetylation gave 2-methylamino-4-methylthiazole-5-carboxylic acid, which was then converted into esters. The ethyl ester and anilide of thiazole-2-carboxylic acid were used as starting compounds for the synthesis of 2-dimethylaminoformimino- and 2-chlorobenzenesulfonylureido derivatives.

The action o[" salt.; o f N-monosubstituted dithiocarbamic acids on ct-chloroacetoaeetic ester and the corresponding anilide led to the isolation o[" the ct-dithiocarbamoyl derivatives. These derivatives are converted, on standing or heating, to the ethyl ester and anilide q['4-methyl-3-methyl(ao,l)-2-thiooxy-l,3thiazolyl-5-carboxylic acids, which can be converted to the corresponding acid, acid chloride, and anilide.

We have studied the temperature dependence of the 1H NMR spectra of some 2,4,6-trisubstituted 1,3,5-triazines having an NHAlk or NAlk2 group or groups at the position 2 or 2 and 4 of the heterocycle. We have shown that rotation of these groups about the C-N bond is hindered. We have calculated the free energies of activation for the rotation processes.

It was shown that oxazolopyrimidinium and sym-triazinium chlorides give N(3)-(2-Y-ethyl)-substituted azines with nucleophiles. Oxazolo-sym-triazine also reacts analogously, being converted by hydrogen chloride to the N(3)-(2-chloroethyl) derivative.

A procedure was developed for the synthesis of (4-hydroxy-2-methylquinolin-3-yl)acetic acid and the corresponding acyl chloride. Reactions of the latter with o-aminobenzenethiol, o-phenylenediamine, o-aminophenol, anthranilic acid, and thiosemicarbazide gave, respectively, 2-(4-hydroxy-2-methylquinolin-3-ylmethyl)-1,3-benzothiazole, -benzoxazole, -benzimidazole, 2-(4-hydroxy-2-methylquinolin-3-ylmethyl)-4H-3,1-benzoxazin-4-one, and 4-hydroxy-2-methyl-3-(5-sulfanyl-1H-1,2,4-triazol-3-ylmethyl)quinoline.

From 4-hydroxy-2-methylquinoline-3-propionyl chlorides hydrochlorides the corresponding thiosemicarbazides were synthesized. The cyclization of the latter both in alkaline and acidic media furnished 4-hydroxy-2-methyl-3-[2-(5-mercapto-1H-1,2,4-triazol-3-yl)ethyl]quinolines. The reaction of the above propionyl chlorides with anthranilic acid afforded the corresponding 2-[2-(4-hydroxy-2-methyl-3-quinolyl)ethyl]-4H-3,1-benzoxazin-4-ones.

The reaction of a mixture of formaldehyde and sodium cyanide or of lactic acid nitrile with trimethyl(6-methoxy-4-methylpyrimidinyl-2)ammonium chloride give the 2-(6-methoxy-4-methylpyrimidinyl-2-oxy)alkanoic acid nitriles. They were subsequently converted to the corresponding alkyl esters by a Pinner reaction and then to their 2-(5-halo-6-methoxy-4-methylpyrimidinyl-2-oxy) derivatives using N-halosuccinimides.

It was established that the action of ethyleneimine on mercapto- and cyanamino-sym-triazines gives 2-aminoethylthio- and iminoimidazolidinyl-sym-triazines. The latter are also obtained from salts of cyanamino-symtriazines with ethylenediamine by heating. The 2-aminoethylthio derivatives were tosylated and phenylcarbamoylated.

The reactions of (4-methyl-6-methoxy-2-pyrimidyl)trimethylammonium chloride with a mixture of formaldehyde and sodium cyanide and mixtures of sodium cyanamide and guanidine derivatives in the presence of alkali lead to the formation of 2-substituted pyrimidines.

4-Amino-, 4-methoxy-, 4-methylthio-, 4-alkylamina-, and 4-dialkylamino-6-alkyl(dialkyl)amino-2-(2-chloro-ethoxy)-sym-triazines and the corresponding 2-(2-chloroethylamino)-sym-triazines were obtained. Their cyclization led to the sym-triazinium chlorides or imidazo-sym-triazines.

The 2-amino-4-(2-chlorethoxy)-6-methyl- and 2-(2-chlorethoxy)-4-methoxy-6-methylpyrimidines were synthesized. Depending on the position of the chlorethoxy group in the ring, their therniolysis results in the formation of the oxazolopyrimidinium chloride or the N(1)-(2-chlorethyl) derivative.

Treatment of 2-(N-potassium-N-cyanamino)-4,6-dimethylpyrimidine with ethyliodoacetate produces 2-(N-cyano-N-carbethoxymethylamino)-4,6-dimethylpyrimidine. Alkaline hydrolysis of the last gives 2-(3-potassium-2,4-dioxoimidazolidinyl-1)-4,6-dimethylpyrimidine. Ammonolysis and hydrazinolysis give imino- or amino-imidazolidinylpyrimidine, respectively.

Thermal cyclization of ethyl α-(2-chloro-2-propenyl)-β-arylaminocrotonates in mineral oil afforded the corresponding substituted 2,4-dimethylfuro[3,2-c]quinolines instead of the expected 4-hydroxy-2-methyl-3-(2-chloro-2-propenyl)quinolines.

Two 2-dialkylamino-4-(2-chloroethoxy)-6-methoxyamino-sym-triazines were synthesized. It was established that when they are heated at 120° C, the 2-chloroethoxy group undergoes rearrangement with cyclization to give 2-dialkylamino-4-oxo-8-methoxy-6, 7-dihydroimidazo [1,2-a]-sym-triazines, the structure of which was confirmed by data from the IR, PMR, and mass spectra.

2-(2-Chloroethoxy)-4-N-methyl-N-cyanoamino-6-dialkylamino-sym-triazines were synthesized. It was established that thermolysis of the indicated compounds in xylene is accompanied by dechloroalkylation; however, it takes place at the site of both the dialkylamino and alkylcyanoamino groups to give a mixture of two imidazo-sym-triazines. The structures of the latter were confirmed by data from the IR, PMR, and mass spectra.

2,2-Aminoethoxy-sym-triazines have been synthesized by reduction of cyanomethoxy-sym-triazines or by the reaction of sodium 2-aminoethoxide with quaternary ammonium salts of sym-triazines. Their structures have been established by PMR and mass spectral examination.