Benzophenone ketals

All the procedures described were performed using dry solvents which were freshly distilled under nitrogen. Tetrahydrofuran and ether were distilled from sodium benzophenone ketal under nitrogen, and dichloromethane from calcium hydride under nitrogen. Petroleum ether (b.p. 40-60 °C) was distilled. Starting materials and solvents were used as obtained from commercial suppliers without further purification unless specified otherwise. 

The benzophenone ketal of DIOP (Compound 23) could not be made directly from the corresponding diol but was prepared as follows ... 

Naphthaldehyde Acetal, 342 9-Anthracene Acetal, 343 Benzophenone Ketal, 344 Di-(p-anisyl)methylidene Ketal, 344 Xanthen-9-ylidene Ketal, 344 2,7-Dimethylxanthen-9-ylidene Ketal, 344... 

We have also tested the stereodirecting effect of the benzophenone moiety in a-glucosylation, using thioglucosides as donors that were activated with N-iodosuccinimide and trimethylsilyl trifluoromethanesulfonate. In Table II, the data show excellent yields of the desired disaccharides, combined with high a-stereoselectivity. Interestingly, when the donors 10 and 12 were used in a less than equimolar amount, the a-selectivity increased (items 1, 3) relative to the experiments having the donor 10 and acceptors 11 and 14 in a 3 1 molar ratio (items 2, 5). The benzophenone ketal-protected donors 10 and 12 (items 1, 3)... 

Table I. 4,6-0-Benzophenone ketals as stereodirecting moieties in 1,2-cis glucosaminylation...

Keta.Is, Trimethylpentanediol reportedly forms a cycHc ketal by heating it with benzophenone ia the presence of sulfonic acid catalysts at reflux temperatures ia toluene (64). These are said to be useful as aprotic solvents for ink-jet printing and as inflammation inhibitors for cosmetic preparations... 

The chemistry involved in LfV-curable resin systems has been extensively investigated and thoroughly surveyed [88-94]. LfV-radiation polymerization, is in principle, completely analogous to the conventional addition polymerization. A photoinitiator is used in UV polymerization. Its function is the same as the free-radical initiator. A conventional initiator possesses a thermally labile bond which is cleaved to form free-radical species, but the photoinitiator has a bond which breaks upon absorption of radiant energy. Benzoin ethers, benzyldialkyl ketals, benzophenone, and acetophenone derivatives are the important LfV-photoinitiators [95-99]. 

A similar situation may be obtained when alkali metals are immersed in ultrapure ethers containing benzophenone [53], The metal thus dissolves via formation of stable ketal radical anions in solution (and metal ions as well). It should be emphasized that the above processes occur even when the active metal is initially introduced into the solution covered by surface films (due to reactions with atmospheric contaminants). We assume that electron tunneling through the films enables the initiation of the dissolution process. This process breaks the film on the metal (as metal is depleted beneath the rigid surface film), thus enabling solvent molecules to reach the active surface and solvate more electrons. This increases the metal solubilization and the further breakdown of the initial surface films. Hence, an equilibrium between a bare metal and the blue solution can finally be reached, as explained above (Eq. 13). 

Second-order rate coefficients, kH (= rate/[S] [H30+]), for the hydrolyses of some typical acetals, ketals, and orthoesters in purely aqueous solutions are collected in Table 12. In a compilation of data from one single source [162], ftH values can be found for the reactions of a large number of diethyl acetals and ketals in 50 % dioxane—water at 25 °C. In more recent studies, kH values have been determined for the hydrolyses of substituted benzaldehyde diethylacetals [163] and benzophenone diethyl-ketal [164] in the same solvent (Table 13). The hydrolyses of para-substituted methyl orthobenzoates have been studied in 70 % methanol-water [169]. A large amount of other work is concerned with various special examples. 

Kinetic data are available for the hydrolysis of benzophenone diethyl ketal in various dioxane—water mixtures [164]. General catalysis cannot be detected with certainty [165, 188,189]. The activation parameters for the H30+ catalyzed reaction are AH = 13.9 kcal. mole-1 and AS = +1.4 eu as expected for an A1 reaction. Another interesting example is the acid catalyzed hydrolysis of the tetramethyl ketal of p-benzoquinone which takes place in two stages [190]... 

The A-benzyloxycarbonyl group, which cannot be removed electrochemically in methanol, may be cleaved in DMF [40]. i/ -esters, such u-benzoylbenzoic acid V -ethyl ester, which is an acylated ketal of a benzophenone, may be reduced in an acetate buffer to a phthalide [71]. 

HOCH2CH2OH, (i-PrO)3CH, RhCl3(fnp/t( j.s ), [triphos - H3CC(CH2PPh2)3], rt, reflux, 80-100% yield. Benzophenone, which normally does not react well, can be ketalized using this method. 

Photoisomerization Cyclopentadienone ketals. Mercuric oxide, see Nickel carbonyl. Photoreduction, under p-Boronobenzoic acid, see 1,8-Naphthalylnaphthalene. Sodium sulfite. Photosensitizer Benzophenone (see 2-Diazapropane). Methylene blue (see Formamide). 

Formation of intermediate chloro derivative 112 was confirmed by its hydrolysis to benzophenone and alcoholysis to corresponding dimethyl ketal. Reaction of CBT with diazomethane resulting in formation of 1- and 2-chloromethylbenzotriazoles also confirms the proposed reaction scheme. 

The 3,4-ketal of 3,4,5-trihydroxybenzoic acid (gallic acid) with benzophenone in the form of its 2,3-diacylpyranyl derivative upon treatment in dichloromethane and pyridine containing lead tetraacetate at 0°C afforded a coupled product (in diastereoisomerically pure form) at the 6,6 -positions of the adjoining aromatic rings in 79% yield (ref.36). One of four possible forms is shown. 

Acetophenone is converted in this way into the diethylene ketal in 74% yield. Under the same conditions benzophenone is unreactive. The reagent appears particularly useful for preparation of acetals of aromatic ortho-hydroxy aldehydes. Ketalization of A -3-keto steroids is accompanied by migration of the double bond [(1) (2)]. The tetrathio orthocarbonate (3) can be used in the... 

This reaction can be done in the presence of a rather Wide range of functionality. It has been used with aromatic compounds such as 2-furylmethanol derivatives, as in the reaction of 382 with benzophenone to give a 65% yield of 383 along with a 20% yield of 384.322 -ghg photocycloaddition product of the Paterno-Biichi reaction with these substrates is an acetal or a ketal, and it can be hydrolyzed to produce acyl derivatives or other functionality. This synthetic route is attractive since achiral fragments generate cycloadducts with several contiguous chiral centers whose relative stereochemistry can usually be predicted with great accuracy. 

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