Disubstituted-l,3-dioxanes

The conformations of three 2,2 -disubstituted-l,3-dioxane derivatives 65-67 have been elucidated by NMR spectroscopy <1998CHE141, 1999PAC385, 2001ARK(xii)7> only the conformers with the more polar substituent in an axial position have been assessed as being in agreement with the anomeric effect. 

The erythrolthreo-KoracK of three 4,5-disubstituted-l,3-dioxanes 73 (cf. Table 5), synthesized as chiral building blocks based on the 1,3-dioxane core, were assigned by H NMR spectroscopy (Table 5) <1999TA139> additionally, they are enantiomerically pure. 

As mentioned above, since the ROP of cyclic carbonates is an equilibrium reaction, six-membered cychc carbonates show a strong substitution effect on the equihbrium monomer concentration. The anionic ROP of l,3-dioxan-2-one (2) and 5,5-disubstituted l,3-dioxan-2-ones (10, 11, 12, 14) in THF solution using potassium tert-butoxide as initiator revealed an increasing monomer concentration at... 

Dioxo-l,3-dioxanes ring-open under basic conditions. Cleavage of the 5,5-disubstituted derivatives in the presence of quininium or quinidinium alkoxides produces chiral malonic hemi-esters (ee 30-40%) in high yield [11]. The addition of cetyltrimethylammonium bromide promotes the base-catalysed cleavage of p-keto esters to form ketones under sonication [12]. 

Dimethyl-l,3-dioxan-5-one SAMP/RAMP hydra-zones j were used as dihydroxyacetonephosphate equivalents in the synthesis of C2 symmetric ketones (eq 5), aza sugars with novel substitution patterns, or C5 to C9 deoxy sugars. SAMP hydrazones of 2-oxo esters represent novel phosphoenolpyruvate (PEP) equivalents. a,a-Disubstituted spiroacetals are accessible via the alkylation of ketone SAMP/RAMP hydrazones. ... 

Disubstituted l,3-thiazine-4,6-diones 168 (R1 = Ph R2 — Et, Br, N02) exist in DMSO and dioxane solution, in crystal and in the gas phase preferentially as enol tautomers 168a. Other tautomeric forms were detected only in the gas phase (95ZOB926). 

The lipase-catalyzed polymerization of the disubstituted TMC analog 5-methyl-5-benzyloxycarbonyl-l,3-dioxan-2-one (MBC) was also studied [89]. The bulk polymerization, catalyzed by Pseudomonas fiuorescens lipase for 72 h at 80 °C, gave 97% monomer conversion and product in 97% yield with M = 6100. The benzyl... 

As in many other areas of 1,3-oxazine chemistry, ketenes and isocyanates generated in situ are often used to prepare oxazin-6-ones. For example, 2,4-disubstituted l,3-oxazin-6-ones (135) are readily available through the thermolysis of 5-[(A-acylamino)alkylidene]-l,3-dioxane-4,6-diones (134). The latter are generated from the reactions of the appropriate ethyl acylimidate (133) and Meldrum s acid (Scheme 36) <86CPB1980>. Similarly, the bismethylthiomethylene derivative (136) reacts with benzamides in the presence of potassium hydroxide to afford the methyl-thioacylaminomethylene derivatives (137 R = MeS), which can be reacted further with ammonia to give the amino compounds (137 R = NHj). In turn, these products can be thermolyzed to afford the oxazinones (138 R = MeS) or (138 R = NH2), respectively (Scheme 37) <91SC1213>. 

Heterocyclizations. Hemiacetals derived from 5-hydroxy-2-alkenoic esters under basic conditions can cyclize to form l,3-dioxanes. This method is suitable for the synthesis of iyn-1,3-diol units. The base-catalyzed reaction of 2-hydroxymethyl 1,3-enynes and the thiol analogs provide furans and thiophenes. 2,3-Disubstituted furans are accessible from isomeric enynes, by way of an 5 2 reaction. 

Besides the fully unsaturated 5 f-l,4-dioxepin (45), the unsaturated 1,4-dioxepins, 6,7-dihydro-5Ef-l,4-dioxepin (46), and 2,3-dihydro-5 f-l,4-dioxepin (47), incorporate either the structural feature of an enediol ether or an enol ether. One general method for the preparation of seven-membered rings of type (46) involves ring expansion thus, treatment of 2-(methoxymethyl)-l,3-dioxane with dodecylbenzenesulfonic acid in vacuum gas oil at 250 °C and simultaneous distillation gave (46) with 69% conversion and 84% selectivity. Several 6,6-disubstituted derivatives (49), which have found interest as intermediates for agrochemicals, drugs, and plastics, have analogously been... 

Smith utilized Petasis-Ferrier rearrangement [17] in the total syntheses of zampanoUde (Sect. 3.2.1) and phorboxazole [18,19]. The l,3-dioxan-4-ones 11 are transformed into 4-methylene-1,3-dioxanes 12, which are treated with Lewis acids to give oxonium intermediates 13. like the Prins reaction described above, the cfs-2,6-disubstituted tetrahydropyran-3-ones 14 are preferentially synthesized via the C - C bond formation (Scheme 5). 

Lemieux, R. U., and S. Koto The Conformational Properties of Glycosidic Linkages. Tetrahedron 30, 1933 (1974) Bailey, W. F., and E. L. Eliel Conformational Analysis. XXIX. 2-Substituted and 2,2-Disubstituted 1,3-Dioxanes. The Generalized and Reverse Anomeric Effects. J. Amer. Chem. Soc. 96, 1798 (1974) Anet, F. A. L., and I. Yavari Generalized Anomeric Effect and Barrier to Internal Rotation about the Oxygen-Methylene Bond in Chloromethyl Ether. J. Amer. Chem. Soc. 99, 6752 (1977). 

A similar reaction of 5-methylene-l,3-dioxan-2-one with varying amounts of aldehydes afforded monocarbonyl allylation product 1-substituted 2-methylenealkan-l,4-diol or double-carbonyl allylation product 1,5-disubstituted 3-methylenealkan-l,5-diol (eq 54). ... 

In addition to simple linear a-olefms. Park et reported the polymerization of a number of 1,6-dienes catalyzed by palladium complexes to afford polymers with trans-1,2-disubstituted five-membered rings. In a subsequent report, 114/NaBArF4 was shown to polymerize 5-allyl-5-aotyl-2,2-dimethyl-l,3-dioxane in a living fashion (Scheme 20). A linear inaease in M with monomer conversion was... 

Cyclopenta[fc]dioxanes (44) are accessible from the reaction of the dioxenylmolybdenum carbene complex (43) with enynes <96JOC159>, whilst an intramolecular and stereoselective cyclisation of (Ti5-dienyl)tricarbonyliron(l+) cations affords chiral frans-2,3-disubstituted 1,4-dioxanes <96JOC1914>. 2,3-Dimethylidene-2,3-dihydro-1,4-benzodioxin is a precursor of the 3,8-dioxa-lff-cyclopropa[i]anthracene, which readily dimerises to dihydrotetraoxaheptacene (45) and the analogous heptaphene <96AJC533>. 

Similarly, using either sulfuric acid, the SOs/dioxane complex, or a solution of SO3 in chloroform/dioxane, 4,6-diphenyl-l,2-oxathiin 2,2-dioxide was obtained from phenyl acetylene <1999RJ0415>, 3,6-disubstituted-l,2-oxathiane 2,2-dioxides were obtained from allylphenol <2002RJ01210>, and 3,4-dihydro-6-phenyl-l,2-oxathiin-4-one 2,2-oxide was obtained from Ph-CO-CH2-COMe <1991CIL253>. 

Functionalised 2,3-dihydro-l,4-dioxins can be synthesised in a three step-sequence from P-keto esters. The key step is the insertion of a Rh-carbenoid derived from an a-diazo-p-keto ester into an 0-H bond of a 13-diol <99H(51)1073>. The reaction of 2-(l,4-dioxenyl)alkanols with silyl enol ethers yields 23-disubstituted 1,4-dioxanes. When 13-bis(trimethylsilyloxy)-cyclobut-l-ene is used, the expected cyclobutanone products are accompanied by a spirocyclopropane derivative <99TL863>. 1,4-Dioxane-monochloroborane 57 is a highly reactive hydroborating reagent <990L315>. 

Calamitic compounds which exhibit a smectic and/or nematic phase usually consist of a relatively rigid central core containing co-linear six-membered rings, either aromatic rings, such as 1,4-disubstituted-phenylene, 2,5-disubstituted-pyridine, 2,5-disubstituted-pyrimidine, 3,6-disubstituted-pyridazine, and alicyc-lic rings, such as /ra j-l,4-disubstituted-cyclohexane, 1,4-disubstituted-bicy-clo[2.2.2]octane, 2,5-disubstituted-dioxane. Heteroaromatic rings tend to lead to the formation of smectic phases rather than the nematic phase unless combined with a polar terminal function, such as a cyano group. The dependence of the liquid crystalline transition temperatures on the nature of... 

A slow cleavage of a benzylic C-O bond is observed in the reduction in DMF of 2-disubstituted 4-(4 -nitrophenyl)-l,3-dioxolanes and dioxanes the hemiketal thus formed is hydrolyzed to the ketone so these compounds may be used as protecting groups for ketones. On preparative reduction besides ketone some side products, formed by attack by the EGB promoted substrate anion on DMF, were isolated [79]. 

Disubstituted-1,3,2-dioxaborinanes, 4.5, are structurally similar to 2,5-disubsti-tuted-1,3-dioxanes but without the complication of cis-/fra s-isomerism the creation of the dioxaborinane ring is achieved by esterification of a 2-substituted-propan-1,3-diol with an arylboronic acid [62, 63]. For compounds of this type with a 5-aryl substituent, 2-arylpropan-l,3-diols are required and are prepared by coupling the ethyl cyanoacetate anion and a 4-substitut-ed-phenyl bromide or iodide [62] and the 5-alkyl-substituted-1,3,2-dioxaborinanes [63] are obtained from 2-alkylpropan-1,3-diols (4.1). 

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