Regio- and stereoselectivity in the Lewis acid- and NaH-induced reactions of thiocamphor with (R)-2-vinyloxirane

The reaction of the enolizable thioketone (1R,4R)-thiocamphor (=(1R,4R)-1,7,7-trimethylbicyclo[2.2.1]heptane-2-thione; 1) with (R)-2-vinyloxirane (2) in the presence of a Lewis acid such as SnCl4 or SiO2 in anhydrous CH2Cl2 gave the spirocyclic 1,3-oxathiolane 3 with the vinyl group at C(4’), as well as the isomeric enesulfanyl alcohol 4. In the case of SnCl4, an allylic alcohol 5 was obtained in low yield in addition to 3 and 4 (Scheme 2). Repetition of the reaction in the presence of ZnCl2 yielded two diastereoisomeric 4-vinyl-1,3-oxathiolanes 3 and 7 together with an alcohol 4, and a ‘1 :2 adduct’ 8 (Scheme 3). The reaction of 1 and 2 in the presence of NaH afforded regioselectively two enesulfanyl alcohols 4 and 9, which, in CDCl3 , cyclized smoothly to give the corresponding spirocyclic 1,3-oxathiolanes 3, 10, and 11, respectively (Scheme 4). In the presence of HCl, epimerization of 3 and 10 occurred to yield the corresponding epimers 7 and 11, respectively (Scheme 5). The thio-Claisen rearrangement of 4 in boiling mesitylene led to the allylic alcohol 12, and the analogous [3,3]-sigmatropic rearrangement of the intermediate xanthate 13, which was formed by treatment of the allylic alcohol 9 with CS2 and MeI under basic conditions, occurred already at room temperature to give the dithiocarbonate 14 (Schemes 6 and 7). The presented results show that the Lewis acid-catalyzed as well as the NaH-induced addition of (R)-vinyloxirane (2) to the enolizable thiocamphor (1) proceeds stereoselectively via an SN2-type mechanism, but with different regioselectivity

cis-(6RS,13RS)-3,3,10,10-Tetramethyl-6,13-diphenyl-1,8-dioxa-4,11-diazacyclotetradecane-2,5,9,12-tetraone and two of its precursors

The title macrocycle, C26H30N2O6, (VI), was obtained by ;direct amide cyclization' from the linear precursor 3-hydroxy-N-[1-methyl-1-(N-methyl-N-phenylcarbamoyl)ethyl]-2-phenylpropanamide, the N-methylanilide of rac-2-methyl-2-[(3-hydroxy-2-phenylpropanoyl)amino]propanoic acid, C13H17NO4, (IV). The reaction proceeds via the intermediate rac-2-(2-hydroxy-1-phenylethyl)-4,4-dimethyl-1,3-oxazol-5(4H)-one, C13H15NO3, (V), which was synthesized independently and whose structure was also established. Unlike all previously described analogues, the title macrocycle has the cis-diphenyl configuration. The 14-membered ring has a distorted rectangular diamond-based [3434] configuration and intermolecular N-H...O hydrogen bonds link the molecules into a three-dimensional framework. The propanoic acid precursor forms a complex series of intermolecular hydrogen bonds, each of which involves pairwise association of molecules and which together result in the formation of extended two-dimensional sheets. The oxazole intermediate forms centrosymmetric hydrogen-bonded dimers in the solid state

Thermolysis of imidates: A new method for the generation of carbonyl ylides

Thermolysis of dimethyl 2-[(3-oxo-3H-isoindol-1-yl)oxy]malonate (8) promotes a [1,4]-H shift in the imidic N¼C O CH fragment of the starting molecule, which leads to a reactive carbonyl ylide. This carbonyl ylide can be trapped by the C¼N bond of imidates and imines, as well as the C¼O bond of benzaldehyde. The corresponding cycloadducts 11, 14, and 16 are formed regioselectively in good yields (60 – 95%) and with high stereoselectivity. In the case of 11, the minor cycloadduct in solution undergoes an isomerization to give the more stable stereoisomer. The structures of two cycloadducts, i.e., 11a and 14a, have been established by X-ray crystallography

Thia- and selenaheterocycles by a four-component reaction using elemental sulfur and selenium

The course of the four-component reactions of (2-benzimidazolyl) acetonitrile, carbondisulfide, isothiocyanate, and sulfur and selenium, respectively, is quite different. Whereas in the case of sulfur a tetracyclic [1,3]thiazolo[4 ,5 :4,5]pyrimido[1,6-a]benzimidazol-2(3H)-thione is formed, a zwitterionic 7-(benzimidazolium-2-yl)-[1,2]thiaselenolo[2,3-b][1,2,4]thiaselenazole-6-thiolate (an azaselenadithiapentalene) is the product in the case of selenium. The structures of the products have been established by X-ray crystallography, and reaction mechanisms for their formation are proposed

Limitations of balloon sinuplasty in frontal sinus surgery

Balloon sinuplasty is a tool that is used to treat selected patients with paranasal sinus pathologies. No studies have investigated the aetiology of failed access to the frontal sinus. The aim of our study was to specify the intraoperative technical failure rate and to analyse the aetiology of the failed access to predict potential technical difficulties before surgery. We retrospectively analysed the charts of patients who underwent balloon sinuplasty from November 2007 to July 2010 at three different ENT-Centres. CT-analysis of the patients with failed access was performed. Of the 104 frontal sinuses, dilation of 12 (12%) sinuses failed. The anatomy of all failed cases revealed variations in the frontal recess (frontoethmoidal-cell, frontal-bulla-cell or agger-nasi-cell) or osteoneogenesis. In one patient, a lymphoma was overlooked during a balloon only procedure. The lymphoma was diagnosed 6months later with a biopsy during functional endoscopic sinus surgery. In complex anatomical situations of the frontal recess, balloon sinuplasty may be challenging or impossible. In these situations, it is essential to have knowledge of classical functional endoscopic sinus surgery of the frontal recess area. The drawbacks of not including a histopathologic exam should be considered in balloon only procedure

Reactions of alpha,beta-unsaturated Thioamides with Diazo compounds

Several reactions of the a,b-unsaturated thioamide 8 with diazo compounds 1a–1d were investigated. The reactions with CH2N2 (1a), diazocyclohexane (1b), and phenyldiazomethane (1c) proceeded via a 1,3-dipolar cycloaddition of the diazo dipole at the C=C bond to give the corresponding 4,5-dihydro-1H-pyrazole-3-carbothioamides 12a–12c, i.e., the regioisomer which arose from the bond formation between the N-terminus of the diazo compound and the C(alpha)-atom of 8. In the reaction of 1a with 8, the initially formed cycloadduct, the 4,5-dihydro-3H-pyrazole-3-carbothioamide 11a, was obtained after a short reaction time. In the case of 1c, two tautomers 12c and 12c’ were formed, which, by derivatization with 2-chlorobenzoyl chloride 14, led to the crystalline products 15 and 15’. Their structures were established by X-ray crystallography. From the reaction of 8 and ethyl diazoacetate (1d), the opposite regioisomer 13 was formed. The monosubstituted thioamide 16 reacted with 1a to give the unstable 4,5-dihydro-1H-pyrazole-3-carbothioamide 17

Synthesis of Bis-Heterocyclic 1H-Imidazole 3-Oxides from 3-Oxido-1H-imidazole-4-carbohydrazides

The reaction of 1H-imidazole-4-carbohydrazides 1, which are conveniently accessible by treatment of the corresponding esters with NH2NH2·H2O, with isothiocyanates in refluxing EtOH led to thiosemicarbazides (= hydrazinecarbothioamides) 4 in high yields (Scheme 2). Whereas 4 in boiling aqueous NaOH yielded 2,4-dihydro-3H-1,2,4-triazole-3-thiones 5, the reaction in concentrated H2SO4 at room temperature gave 1,3,4-thiadiazol-2-amines 6. Similarly, the reaction of 1 with butyl isocyanate led to semicarbazides 7, which, under basic conditions, undergo cyclization to give 2,4-dihydro-3H-1,2,4-triazol-3-ones 8 (Scheme 3). Treatment of 1 with Ac2O yielded the diacylhydrazine derivatives 9 exclusively, and the alternative isomerization of 1 to imidazol-2-ones was not observed (Scheme 4). It is important to note that, in all these transformations, the imidazole N-oxide residue is retained. Furthermore, it was shown that imidazole N-oxides bearing a 1,2,4-triazole-3-thione or 1,3,4-thiadiazol-2-amine moiety undergo the S-transfer reaction to give bis-heterocyclic 1H-imidazole-2-thiones 11 by treatment with 2,2,4,4-tetramethylcyclobutane-1,3-dithione (Scheme 5)

Alpha-Adrenergic Mechanisms in the Cardiovascular Hyperreactivity to Norepinephrine-Infusion in Essential Hypertension.

Aims Essential hypertension (EHT) is characterized by cardiovascular hyperreactivity to stress but underlying mechanism are not fully understood. Here, we investigated the role of α-adrenergic receptors (α-AR) in the cardiovascular reactivity to a norepinephrine (NE)-stress reactivity-mimicking NE-infusion in essential hypertensive individuals (HT) as compared to normotensive individuals (NT). Methods 24 male HT and 24 male NT participated in three experimental trials on three separate days with a 1-min infusion followed by a 15-min infusion. Trials varied in infusion-substances: placebo saline (Sal)-infusions (trial-1:Sal+Sal), NE-infusion without (trial-2:Sal+NE) or with non-selective α-AR blockade by phentolamine (PHE) (trial-3:PHE+NE). NE-infusion dosage (5µg/ml/min) and duration were chosen to mimic duration and physiological effects of NE-release in reaction to established stress induction protocols. We repeatedly measured systolic (SBP) and diastolic blood pressure (DBP) as well as heart rate before, during, and after infusions. Results SBP and DBP reactivity to the three infusion-trials differed between HT and NT (p's≤.014). HT exhibited greater BP reactivity to NE-infusion alone compared to NT (trial-2-vs-trial-1: p's≤.033). Group differences in DBP reactivity to NE disappeared with prior PHE blockade (trial-3: p=.26), while SBP reactivity differences remained (trial-3: p=.016). Heart rate reactivity to infusion-trials did not differ between HT and NT (p=.73). Conclusion Our findings suggest a mediating role of α-AR in DBP hyperreactivity to NE-infusion in EHT. However, in SBP hyperreactivity to NE-infusion in EHT, the functioning of α-AR seems impaired suggesting that the SBP hyperreactivity in hypertension is not mediated by α-AR