Dioxa preparation

Carbocations are intermediates in several kinds of reactions. The more stable ones have been prepared in solution and in some cases even as solid salts, and X-ray crystallographic structures have been obtained in some cases. An isolable dioxa-stabilized pentadienylium ion was isolated and its structure was determined by h, C NMR, mass spectrometry (MS), and IR. A P-fluoro substituted 4-methoxy-phenethyl cation has been observed directly by laser flash photolysis. In solution, the carbocation may be free (this is more likely in polar solvents, in which it is solvated) or it may exist as an ion pair, which means that it is closely associated with a negative ion, called a counterion or gegenion. Ion pairs are more likely in nonpolar solvents. 

Kaliappan and coworkers [249] prepared dioxa-triquinanes 6/3-68 together with the spiro compound 6/3-67 by a domino enyne RCM of the ene-yne 6/3-66 (Scheme 6/3.19). 

Let us now discuss heterocyclic propellanes and dispirans. 8,1 l-Dioxa[4.3.3]propell-3-ene 34 was prepared (in 73% yield) by heating the tetrol 33 with KHS04 at 190-200 °C4e). This was accompanied by the bicyclic ether 35 (10% yield) but no... 

A. Preparation of (2R,3S)- ana (2S,3S)-1,4-dioxa-2,3-dimethyl-2-(1-methyl-ethenyl)-8-carbcethoxy-8-azaspiro[4.5]decane. An oven-dried, 500-mL, three-necked, round-bottomed flask is fitted with a mechanical stirrer, 100-mL addition funnel, and rubber septum, and then is charged with 100 mL of dry tetrahydrofuran (Note 1) and... 

Preparation of 9,9-Dihydro-9-Hydroxyperfluoro-(3,6-Dioxa-5-Methyl-l-Nonene) (5)... 

The structure of UCSB-10 (not shown) involves a 3D 12-MR (7.6 x 7.4 A) system that opens up to large cages. The composition of this structure is Ga36Zn36P720288, but UCSB-10 can also be prepared with Zn, Co, and Mg as gallo-or aluminophosphates. The template for UCSB-10 was 4,9-dioxa-l-12-dode-canediamine. 

Examples of organooxasilacycloalkanes have been presented by Makarova and co-workers.43 2,8-Dichloro-2,4,4,6,6,8,10,10,12,12-decamethyl-5-carbacyclohexasiloxane, 4,7-dichloro-2,2,4,7-tetramethyl-l,3-dioxa-2,4,7-trisila-cycloheptane, and 4,8-dichloro-2,2,4,8-tetramethyl-l,3-dioxa-2,4,8-trisilacyclooctane were prepared for the first time by the heterofunctional condensation of l,l,7,7-tetrachloro-l,3,3,5,5,7-hexamethyl-4-carbatetrasiloxane with... 

As part of a preparation of marine odourants, oxidation by RuCyaq. Na(lO )/ CCl of the =CH3 moiety in the marine floral-aldehyde 1-methyl-7-methylene-2,3,7,8-tetrahydro-l//,6//-5,9-dioxacyclohepta[/]indene gave l-methyl-2,3-di-hydro-l//-5,9-dioxa-cyclohepta[/]-inden-7-one (Fig. 3.16) [200]. 

Hydroxy acids have been protected as acetals which are l,3-dioxan-4-ones. Numerous examples of such dioxa-nones were reported, and they have been widely used in synthetic organic chemistry. In particular, dioxanone triflates prepared from 2,4,6-trihydroxybenzoic acid or analogs were used for several transition metal-catalyzed crosscouplings. A Suzuki coupling <2006EJ01678> and a Stille coupling <2005JOC3686> provide illustrations of this principle (Scheme 93). 

Using a typical poly (vinyl chloride) (PVC)-based membrane with different ionophores - Zn-bis(2,4,4-trimethylpen-tyl) dithiophosphinic acid complex [450], protoporphyrin IX dimethyl ester [451], porphyrin derivative [452] and hemato-porphyrin IX [453], tetra(2-aminophenyl) porphyrin [454], cryptands [455, 456], 12-crown-4 [457], benzo-substituted macro-cyclic diamide [458], 5,6,14,15-dibenzo-l, 4-dioxa-8,l 2, diazacyclopentadecane-5,14-diene [459], and (A-[(ethyl-l-pyrrolidinyl-2 -methyl) ] methoxy-2-sulfamoyl-5 -benza-mide [460] - the sensors for zinc ions were prepared and investigated. The armed macrocycle, 5,7,7,12,14,14-hexamethyl-1,4,8,11 -tetraazacyclo tetradeca-4,11 -diene dihydrogen perchlorate was used for the preparation of polystyrene-based Zn(II)-sensitive electrode [461]. 

The l,3,3,3a,8a-tetrahydro-8-oxa-2-thia- 205, l,3,3,3a,8a-tetrahydro-2,8-dioxa- 206, and 3,3a,8,8a-tetrahydro-12/-2-thia-8-aza-cyclopenta[ ]indene-2,2-dioxide 207 were prepared by Michael addition or radical cyclization from the corresponding sulfones 202-204 and brominated-dehydrobrominated (in the case of 207, after tosylation) to produce 1,5-diheteropentalene systems 208-210, respectively <1997TL5315>. 

Kim s group also prepared the l,12-diphenyl-5,8-dioxa-2,ll-dithidodecane ligand L44 and reacted it with Cul.164 Contrary to our failure to assemble a network with 1,8 bis(phenylthio)octane, L44 containing eight spacer units between the sulfur atoms allowed the construction of a 2D square-grid-type coordination polymer 44. This finding may be rationalized by the enhanced basicity of -S-benzyl vs. -S-phenyl (Scheme 23). 

The reaction of compound 90 with imidoyl halides without added base gives the hydrochloride salts of 1,2,4-thiadiazol-5-imines 95. The corresponding free bases can be liberated from the salts 95 with weak bases such as bicarbonate, but these imines are labile and decompose readily to form the W-cyanamide 96 and sulfur. The free base can be treated in situ with a second electrophile, such as an acid chloride, imidoyl chloride, or aryldiazonium salt, affording pentalene derivatives 97-99. It should be noted that the compound 98 cannot be prepared in a one-pot procedure from compound 90 and 2 equiv of imidoyl chloride in the presence of base, in contrast to the corresponding dioxa compound 91 (Scheme 22) <1981BSB89, 1992JHC1317>. 

Dioxa-, 1,3,2-dithia-, and 1,3,2-oxathiaborolanes 322 can be readily prepared by reaction of bis(diisopropyl-amino)borylacetylenes 320 with the appropriate diol, dithiol, or hydroxythiol (321 X = 0, S) in the presence of 2 equiv of HC1 (Equation 12) <2004EJI4223>. 

The tetraoxa[26]annulenoquinone has been prepared and electrochemically transformed to the corresponding dianion [95TL4401]. The novel l,12-dioxa[12](l,4)naphthylenophane-14-carboxylic acid has been prepared and resolved its (-)-enantiomer was shown to have the -configuration by X-ray analysis [95TA1043]. The readily accessible octamethyl-tetraoxaquaterene reacts with benzyne to yield (5) but could not be converted into the... 

It can be prepared by treatment of 3-amino-2//-azirines (e.g. 3-(dimethyl-amino)-2,2-dimethyl-2//-azirine) with an amino acid or peptide and, finally, with a (u-hydroxyacid. The formation of the oxazolone, VI/121, is observed when VI/120 is treated with acid. The ring enlargement step, the conversion of VI/121 to VI/122, is observed under the same conditions. The transformation of (-)-(R,R)2- 2-[2-(2-hydroxy-2-phenylacetamido)-2-methylpropionato]-2-phenylacetamido -N,N,2-trimethylpropionamide (VI/123) to (-)-(R,R)-3,3,9,9-tetramethyl-6,12-diphenyl-l,7-dioxa-4,10-diazacyclododecane-2,5,8,ll-tetrone (VI/126) in dry toluene/hydrochloric acid at 100° was observed in a 88 % yield. Compounds VI/124 and VI/125 are discussed to be intermediates. In an analogous reaction sequence cyclopeptides can be synthesized [93]. 

The corresponding 9,1 l-dioxa-10-thiahomoprostanoid 263 was synthesized by reaction of the diol 258 with thionyl chloride. When the reaction with thionyl-chloride was carried out with the erythro diol 264 the isomeric 9,1 l-dioxa-10-thiahomoprostanoid 265 with cis side chains was obtained. The 9,11-dithiahomo-prostanoid 267 was prepared by reaction of the epoxide 266 with potassium methyl xanthate. 

Teyssot et al. reported that the Michael addition of bis(nitrogen or sulfur) nucleophiles to divinyl sulfone provided the corresponding macrocyclic adducts in good yields <2003EJ054>. For example, 9 and 10 have been prepared in 82% and 80% yields, by the reaction of divinyl sulfone with bis(2-mercaptoethyl)ether and 4,7-dioxa-l,10-dithiade-cane, respectively. The X-ray structure of 10 was also reported. 

Two dioxa-trithia- and two trioxa-dithiacrown ethers connected to one calix[4]arene unit have been prepared by Sim et al. <2002BKC879>. Macrocycles 165 and 166 have an Ag+ selectivity in metal picrate extraction, but the percentage extractability was lower than those of corresponding monocrown derivatives 155 and 156 due not only to electrostatic repulsion between the two metal ions, but also to an induced conformation change that does not favor binding of the second metal. The extractability is consistent with the result of silver ion-induced chemical shift change upon the complexation. 

Functional l,3-dioxa-2,4,7-trisilacycloheptanes 192 were prepared by the reaction of corresponding silane diols 191 with methyldichlorosilane in the presence of pyridine, as an HC1 acceptor, and diethyl ether, as solvent (Scheme 35). The subsequent reaction of 192 (R1 = Me, Rz = OSi(Me)3) with chlorine in the presence of pyridine afforded chlorosilane 193, which upon treatment with an alcohol gave alkoxide 194. Siloxanes 192-194 were characterized by H, 13C, and 29Si NMR spectroscopic data C1995JOM29, 1996KGS1590>. 

Perfluoroelastomers prepared by Bish [3] and Hung [4] containing roughly 3 wt% of the termonomer perfluoro(8-cyano-5-methyl-3,6-dioxa-l-octene),... 

Perfluoroether monomers 3,5-dioxa-l-heptene, (I), and 3,5,8-trioxa-l-nonene, (II), were prepared by the author [1] and polymerized with tetrafluoroethylene using perfluoropropionyl-peroxide as the reaction initiator. 

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