Acetals structure

These derivatives are prepared to protect a-hydroxy carboxylic acids they are cleaved by acidic hydrolysis of the acetal structure (HCl, DMF, 50°, 7 h, 71% yield), or basic hydrolysis of the lactone. ... 

Common Name 1 S-methylene-Sa-fluoroprednisolone 21-acetate Structural Formula ch ococh,... 

Therapeutic Function Anabolic steroid Chemical Name 17/ -Aceto-3-oxoestra-4,9,11-triene-3-one Common Name Trienolone acetate Structural Formula ... 

With the chemical structure of PbTX-1 finally known and coordinates for the molecule available from the dimethyl acetal structure, we wanted to return to the natural product crystal structure. From the similarities in unit cells, we assumed that the structures were nearly isomorphous. Structures that are isomorphous are crystallographically similar in all respects, except where they differ chemically. The difference between the derivative structure in space group C2 and the natural product structure in P2. (a subgroup of C2) was that the C-centering translational symmetry was obeyed by most, but not all atoms in the natural product crystal. We proceeded from the beginning with direct methods, using the known orientation of the PbTX-1 dimethyl acetal skeleton (assuming isomorphism) to estimate phase... 

The isotropic equivalent thermal parameters are on the whole larger than in the PbTX-1 dimethyl acetal structure or the structure of the natural product. The B values for atoms on the fused ring skeleton range from 4.7 to 12.6 A (mean square amplitudes of 0.059 and 0.16 A ). Curiously, the largest values are associated with C17-C20 of the 9-membered E ring—the ring that adopts two conformations in crystalline PbTX-1. The acyclic atoms do not have appreciably higher thermal parameters, with the exception of hydroxyl 013, which has a B of 22.4 A 2. 

Esterification and acetal formations in aqueous conditions are among the most common reactions in nature because of the common ester bonds and acetal structures in various organic materials in nature. 

The zinc complex formed with V,V -diphenylformamidinate is structurally analogous to the basic zinc acetate structure, as [Zn4(/i4-0)L6], and the basic beryllium acetate structure. It is prepared by hydrolysis of zinc bis(diphenylformamidinate).184 Mixed metal zinc lithium species were assembled from dimethyl zinc, t-butyl lithium, V.iV -diphenylbenzamidine and molecular oxygen. The amidinate compounds formed are dependent on the solvent and conditions. Zn2Li2 and... 

One of the more difficult problems encountered in obtaining a valid assay of formic acid is that of formate ester formation. The formate is derived from the cyclic, hemi-acetal structure which is an equilibrium form of many free sugars in solution. For example, the oxidation of one of the cyclic forms of D-glucose can readily be seen to give a formate ester (as well as a C-formyl group) on the atom originally denoted as C5. It... 

Since these methoxylated and acetoxylated sulfides have an acetal structure, it is expected that Lewis acid catalyzed demethoxylation should generate a carbocation intermediate which is stabilized by the neighboring sulfur atom. In fact, nucleophilic substitution with arenes has been successfully achieved as shown in Scheme 6.7 [43], This procedure is useful for the preparation of trifluoroethyl aromatics. As already mentioned, generation of carbocations bearing an a-trifluoromethyl group is difficult due to the strong electron-withdrawing effect. Therefore, this carbon-carbon bond formation reaction is remarkable from both mechanistic and synthetic aspects. 

Fig. 40. Projection of the zinc acetate structure on the be plane. (From Ref. 215)...

The relationship, between magnitudes of these sensitivity parameters and the reactivity of the system concerned, was explored quantitatively for three sets of acetal structures, and a further linear relationship was found (Kirby and Jones, 1986). Figure 25 shows a plot of the sensitivity parameter against relative reactivity for series of compounds, tetrahydropyranyl-, methoxymethyl- and a-glucosyl-OX, known to react with C-OX cleavage at very different rates (relative rates of hydrolysis approximately 1, 103 5 and 106 5, respectively). The correlation is good for both the intercepts (i.e. the... 

PVC materials are often defined to contain 50% or more vinyl chloride units by weight. PVC is generally a mixture of a number of additives and often other units, such as ethylene, propylene, vinylidene chloride, and vinyl acetate. Structurally similar products, but with differing properties, are made from the chlorination of PE but almost all PVC is made from the polymerization of vinyl chloride. Typical homopolymers are about 400-1000 units long. 

The reaction is usually carried out with an acid catalyst. Acetal formation does not proceed to completion because of isolation of single hydroxyl groups between pairs of acetal structures. The two most important acetals are the formal and butyral (R = H and C3H7, respectively). The applications of poly(vinyl alcohol) and its acetals are described in Sec. 3-14c-2. 

Laureacetal-B (70) is a tricyclic oxetane recently isolated from a marine alga. It has the interesting features of bromine substitution and a cyclic acetal structure. In view of the extreme ease of hydrolysis of 2-methoxyoxetane, it seems surprising that a strained ring cyclic acetal would be isolated from a marine source. Its structure assignment is based on spectral studies and chemical transformations (79CL301). 

It is prepared by the alkaline hydrolysis (saponification) or alcoholysis (ester interchange) of polyvinyl acetate [Structure (5.2)] as shown in Scheme 5.1. 

The method used by Peligot can be extended to carboxylates generally (equation 16). Since the complexes with n > 1 were dried in vacuum at 100 °C before analysis, their degree of hydration has not been established. All have low magnetic moments (jueff = 0.7 BM) so it is likely that they have the acetate structure.157... 

Effect of acetal structure on the diffusivity (Def) in a bead of ion exchanger [508] (Catalyst Dowex 50W-X12 temperature 20°C.)... 

The thermodynamic stability of the binuclear site has been demonstrated by the spontaneous assembly of [Fe20(02CR)2L2] (13) from ferric salts in the presence of water, an alkyl carboxylate salt, and a tridentate nitrogen donor ligand L that can cap an octahedral face on iron (8). Suitable ligands include tris(pyrazolyl)borates and 1,4,7-triazacyclononanes. Structure (13) is in essence a portion of the basic ferric acetate structure. The complexes are excellent physical and structural models of the diiron sites and model some aspects of reactivity including redox activity and interconversion of the oxo and hydroxo bridge. 

Treatment with aqueous sulfuric acid cleaves the MOM protective group (which consists of an acetal structure) to give compound 48. 

The formation of methanolysis product 25 (R = Me) was easily understood in terms of ketene acetal structure 24. However, the isolated thermal product 26 is not directly derived from the ketene acetal 24. It is not unreasonable to suggest that thermal transformation of the [2 + 4] adduct 24 into the [2 + 2] adduct 23 takes place, followed by intramolecular migration of the trimethylsilyl group to afford vinylsiloxane... 

The synthesis of 2-alkylidene-substituted l,3-benzoxathiepan-5-one 267 possessing a 0,V-ketene acetal structure was achieved by heterocyclization of 266 in the presence of BF3 NEt3 (Scheme 82) <2001RCB1255>. The reaction corresponds to a formal type a (0—C—C—C—C—0-C) synthesis. 

The descriptive term alkali-sensitive glycoside has special significance to one concerned with a study of the chemistry of carbohydrate substances, for experience often refutes the generalization that the gly-cosidic linkage is stable to alkalis. The acid-catalyzed hydrolysis of glycosides is well known, and is characteristic of the acetal structure they possess.1 However, it is not practical to assume that most glycosides have... 

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