2- Phenyl-l,3-dioxane

The preferred conformations of both 1-methyl-l-phenylcyclohexane and 2-methyl-2-phenyl-l,3-dioxane have the phenyl group in the axial orientation even though the conformational flee energy of the phenyl group (2.9 kcal) is greater than that for a methyl group (1.8 kcal). Explain. 

Figure 1. Hydrolysis pH-rate profiles of phenyl acetate (lower) and a substituted 2-phenyl-l,3-dioxane (HND). Phenyl acetate profile constructed from data of Mabey and Mill (32), HND profile from data of Bender and Silver (33). Phenyl acetate reacts via specific-acid catalyzed, neutral, and base-catalyzed transformation pathways. The pseudo-first-order rate constant is given by Kobs = K(h+) [H+] + Kn + K(qh-) [0H—]. HND hydrolyzes only via an acid-catalyzed pathway the phenolate anion is some 867 times more reactive than its conjugate acid.

B. P. Roberts and T. M. Smits, Regioselectivity in the ring opening of 2-phenyl-l,3-dioxan-2-yl radicals derived from cyclic benzylidene acetals and comparison with deoxygenation of a carbohydrate diol via its cyclic thionocarbonate, Tetrahedron Lett., 42 (2001) 3663-3666. 

DIMETHYE MINO)-l-METHYL-3-OXO-l-PROPENYL DIMETHYL PHOSPHATE see DGQ875 2-(DIMETHYLAMINO)-N-(((METHYL(((2-PHENYL-l,3-DIOXAN-5-YL)METHOXAQ SULFINYL)AMINO)CARBON X)OXY)-2-OXO-ETHANTMIDOTHIOIC ACID, METHYL ESTER see DPL300... 

The hydrolyses of ortho- and para-hydroxy substituted 2-phenyl-l,3-dioxanes provide an interesting special case with the rate equation [178]... 

Foster and coworkers50 established that benzylidenation under these conditions gives rise to diastereoisomeric 2-phenyl-l,3-dioxane derivatives, indicating that kinetic control is operative. They isolated both diastereoisomers of the 4,6-O-benzylidene derivatives of methyl a-D-gluco- and -galacto-pyranoside (as 2,3-di-O-methyl derivatives). 

When, however, methyl 4,6-0-benzylidene-2,3-di-0-methyl-a-D-gluco- and -galacto-pyranoside were prepared (for the first time) under kinetic control, they found, for each, two benzyl signals,49,50 indicating the presence of both diastereoisomers. The chemical shifts for the diastereoisomers were as shown. The smaller values in each pair are similar to those for axial protons in that chair form of 2-phenyl-l,3-dioxanes having axial protons on the same side of the ring. These isomers are the thermodynamically favored ones. 

Table 2 The yields of axial approach of Grignard reagents to 4-tert-butylcyclohexanone and 2-phenyl-l,3-dioxan-5-one [reproduced from reference 7]...

The chemical shifts have been measured for the benzyl protons of a series of 2-phenyl-l,3-dioxanes and 2-phenyl-l,3-dioxolanes. These shifts appear to be characteristic not only of ring size but also of configuration at carbon atom 2. 

The crystal structures of the thermodynamically less stable (/ )-diastereoisomers of methyl 4,6-O-benzylidene-2,3-di-O-methyl-0(-D-gluco- and -jS-D-galacto-pyrano-sides have been reported. In each the 2-phenyl-l,3-dioxane ring adopts the expected (Eliel, Pure Appl. Chem., 1971, 25, 509) axial phenyl chair.The... 

Isopropenyl-2-oxazoline, 1, and poly(2-isopropenyl-2-oxazoline), 2, were prepared as described in the literature (72). 2-Phenyl-l,3-dioxane-5-yl-carbonic acid, 8c, was prepared through the modification of a literature procedure (75). Dimethyl 2,4-dihydroxyphenylsulfonium triflate, 11, was prepared as described in the literature (74). l,3-bis(diethoxymethyl)benzene was prepared through a... 

For (i ,/ )-form see Threitol, T-100. Opt. inactive (meso-) some derivs. may be chiral (see for example 5-Hydroxy-2-phenyl-l,3-dioxane-4-methanol, H-193). Found in a variety of algae, lichens and fungi. Prod, by Protococcus vulgaris, Trentepohlia iolithus and Aspergillus terreus. Bulk sweetener with good taste props. Also thickenei stabiliser, humectant, etc. in food. Cryst. (MeOH). Mp 121.5°. Bp 329-331° Bpjoo 294-296°. Sweetness ca. 0.7 x sucrose. 

Hydroxyphenyl)-l-deoxy-L-tagatopyranose, D-2 5-Hydroxy-2-pheny 1-1,3-dioxane-4-carboxaldehyde, T-KG 5-Hydroxy-2-pheny 1-1,3-dioxane-4-methanol, H-193 5-Hydroxy-2-phenyl-l, 3-dioxane-4-methanol, T-100... 

In contrast to 2-phenyl-l,3-dioxan-5-one, where nucleophiles add, regardless of their size, from the axial side of the carbonyl group, the same nucleophiles add to 2-phenyl-l,3-dithian-5-one exclusively from the equatorial side, to yield (165). A ring-expansion reaction has been observed when 2-methy 1-2-ethyl-1,3-dithiolan was brominated, giving the dithiin (166). ... 

A more subtle problem is to maximize the yield of a reaction that could be carried out in any of a number of media. Should a reaction be done in a solvent in which the desired product is most or least soluble, for instance The answer is not immediately clear. In fact one must say, It depends. If the reaction is between ions of two soluble salts, the product will precipitate out of solution if it is insoluble. For example, a reaction mixture containing barium, silver, chloride, and nitrate ions will precipitate insoluble silver chloride if the solvent is water, but in liquid ammonia the precipitate is barium chloride. Another example, from organic chemistry, described by Collard et al. (2001) as an experiment suitable for an undergraduate laboratory, is the dehydra-tive condensation of benzaldehyde with pentaerythritol in aqueous acid to yield the cyclic acetal, 5,5-bis(hydroxymethyl)-2-phenyl-l,3-dioxane, 1 ... 

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