Ortho acetic ester

Other ortho-acid derivatives which will not be considered in detail in this chapter are the thio ortho esters, amide acetals, ester aminals, and the ortho amides which have the following structures, respectively, RC(SR)3, RC(OR)2-NR2, RC(OR)(NR2)2, and RC—(NR2)3. 

Through this study we suggest a useful synthetic procedure for good candidate compounds of a new cage-cluster. The ort/io-carboranes are very stable chemicals in this research. Carboranyl acetic ester can be easily introduced to the ortho- carborane skeleton and then many types of cyclisation of carboranyl cluster can be made to occur. The reactivity and reaction mechanism for cyclisation of carborane cluster have been discussed. The mechanisms for boron cluster expansion reaction and cyclisation at carboranyl edge are summarized as follows. 

An example of the formation of an ester of an -4,5-alkenoic acid 164 comes in a synthesis of chrysanthemic acid by Ficini and her group.31 Reduction gives the allylic alcohol 163 and [3,3] Claisen rearrangement with triethyl ortho-acetate gives the product 164 in one step. 

The condensation of 4-hydraziopyrimidie 52 with ortho esters led to the formation of l,2,4-triazolo[4,3-c]- and [l,5-c]pyrimidines, where the reaction was found to be dependent on the structure of the ortho ester (78AJC2505 86TL3127 89JHC687).Thus, the ortho acetate gave the unre-... 

The total synthesis d of 16-desmethoxycarbonylvobasine (129) involves as critical stages a neat introduction of an acetic ester residue by Claisen rearrangement of an ortho-ester, and the cyclization of the acid derived from the product by means of polyphosphoric acid (Scheme 22). The synthesis d " of 15,20-dehydroervatamine (130) involves the gramine alkylation of a 4-piperidone ester to give the amino-ketone (131) which on acetylation, ketol cyclization, and dehydration afforded (130) (Scheme 23). 

Probably unjustly these have been somewhat neglected as protective groups, except perhaps in the carbohydrate field. They are prepared by acid-catalyzed reaction of carbonyl compounds with alkyl thiols or with dithiols. The conditions which have been used include ethanedithiol in acetic acid-boron trifluoride [73], ethane-thiol or -dithiol in the presence of hydrogen chloride [81, 82, 83], or in dioxan in the presence of zinc chloride [84]. An interesting alternative is offered by the reaction of carbonyl compounds with ortho-thioboric esters at room temperature without catalyst [85]. 

During the condensation of ethyl (3-chloro-2-quinoxaloyl)acetate 35a with ortho-formic ester in the presence of AC2O (65-70 °C), the formation of two substances was observed the main chlorine-containing reaction product 36a and a minor chlorine-free compound 38 (Scheme 3.13). The amoimt of compound 38 increased with increase in temperature, and at 100-105 °C it became the main reaction product. It was also shown that compound 36a can be obtained by heating the initial compound 35a with orthoformic ester at a higher temperamre (100-105 °C). The chain 35a 36a 38 was therefore investigated (Eiden and Bachmann 1973 ... 

The ester and catalj st are usually employed in equimoleciilar amounts. With R =CjHs (phenyl propionate), the products are o- and p-propiophenol with R = CH3 (phenyl acetate), o- and p-hydroxyacetophenone are formed. The nature of the product is influenced by the structure of the ester, by the temperature, the solvent and the amount of aluminium chloride used generally, low reaction temperatures favour the formation of p-hydroxy ketones. It is usually possible to separate the two hydroxy ketones by fractional distillation under diminished pressure through an efficient fractionating column or by steam distillation the ortho compounds, being chelated, are more volatile in steam It may be mentioned that Clemmensen reduction (compare Section IV,6) of the hj droxy ketones affords an excellent route to the substituted phenols. 

Pentaerythritol in rosin ester form is used in hot-melt adhesive formulations, especially ethylene—vinyl acetate (EVA) copolymers, as a tackifier. Polyethers of pentaerythritol or trim ethyl ol eth an e are also used in EVA and polyurethane adhesives, which exhibit excellent bond strength and water resistance. The adhesives maybe available as EVA melts or dispersions (90,91) or as thixotropic, one-package, curable polyurethanes (92). Pentaerythritol spko ortho esters have been used in epoxy resin adhesives (93). The EVA adhesives are especially suitable for cellulose (paper, etc) bonding. 

In a series of organic acids of similar type, not much tendency exists for one acid to be more reactive than another. For example, in the replacement of stearic acid in methyl stearate by acetic acid, the equilibrium constant is 1.0. However, acidolysis in formic acid is usually much faster than in acetic acid, due to higher acidity and better ionizing properties of the former (115). Branched-chain acids, and some aromatic acids, especially stericaHy hindered acids such as ortho-substituted benzoic acids, would be expected to be less active in replacing other acids. Mixtures of esters are obtained when acidolysis is carried out without forcing the replacement to completion by removing one of the products. The acidolysis equilibrium and mechanism are discussed in detail in Reference 115. 

Oxygen ortho esters are readily cleaved by mild aqueous acid (TsOH Pyr, H20 NaHS04, 5 1 DME, H2O, 0°, 20 min ) to form esters that are then hydrolyzed with aqueous base to give the acid. Note that a trimethyl ortho ester is readily hydrolyzed in the presence of an acid-sensitive ethoxyethyl acetal. The order of acid stability is... 

Enols of simple ketones can be generated in high concentration as metastable species by special techniques. Vinyl alcohol, the enol of acetaldehyde, can be generated by very careful hydrolysis of any of several ortho ester derivatives in which the group RC02 is acetate acid or a chlorinated acetate acid. ... 

Synthesis of the remaining half of the molecule starts with the formation of the monomethyl ether (9) from orcinol (8). The carbon atom that is to serve as the bridge is introduced as an aldehyde by formylation with zinc cyanide and hydrochloric acid (10). The phenol is then protected as the acetate. Successive oxidation and treatment with thionyl chloride affords the protected acid chloride (11). Acylation of the free phenol group in 7 by means of 11 affords the ester, 12. The ester is then rearranged by an ortho-Fries reaction (catalyzed by either titanium... 

Intermediate 7, a viable precursor of intermediate 6, possesses a y,<5-unsaturated ester, the structural prerequisite, or retron, for the ortho ester Claisen transform.5 In the synthetic direction, the convergent union of intermediates 9 and 10 could give mixed-ketene acetal 8 the intermediacy of 8 should be brief, for it should readily... 

A prominent structural feature of 21 and its precursor 22 is the trans C16-C17 trisubstituted double bond. The particular relationship between the ethoxycarbonyl function and the A16 17 double bond in 22 is significant because it satisfies the structural prerequisite for the Johnson ortho ester Claisen rearrangement transform.2130 Mixed ketene acetal 23 thus emerges as the immediate... 

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