Acetate derivatives

Analysis the functional group is an acetal derived fiom alcohols and a carbonyl compound. 

Unusual cyclocarbonylation of allylic acetates proceeds in the presence of acetic anhydride and an amine to afford acetates of phenol derivatives. The cinnamyl acetate derivative 408 undergoes carbonylation and Friedel-Crafts-type cyclization to form the a-naphthyl acetate 410 under severe condi-tions[263,264]. The reaction proceeds at 140-170 under 50-70 atm of CO in the presence of acetic anhydride and Et N. Addition of acetic anhydride is essential for the cyclization. The key step seems to be the Friedel-Crafts-type cyclization of an acylpalladium complex as shown by 409. When MeOH is added instead of acetic anhydride, /3,7-unsaturated esters such as 388 are... 

The (l-ethynyl)-2-propenyl acetate derivative 111 undergoes an interesting PdCl2(PhCN)2-catalyzed cyclization to form the 2-cyclopentenone 112[47], A Pd-carbene complex is assumed to be an intermediate of the formation of 112. 

Diols that bear two hydroxyl groups m a 1 2 or 1 3 relationship to each other yield cyclic acetals on reaction with either aldehydes or ketones The five membered cyclic acetals derived from ethylene glycol (12 ethanediol) are the most commonly encoun tered examples Often the position of equilibrium is made more favorable by removing the water formed m the reaction by azeotropic distillation with benzene or toluene... 

Write the structures of the cyclic acetals derived from each of... 

Isotope incorporation experiments have demonstrated the essential correctness of the scheme presented m this and preceding sections for terpene biosynthesis Considerable effort has been expended toward its detailed elaboration because of the common biosyn thetic origin of terpenes and another class of acetate derived natural products the steroids... 

The addition of certain glycols and polyols to acroleki leads to the production of cycHc acetal derivatives. 

Introduction of Nitrogen into a Terpenoid Skeleton. The acetate-derived fragments (35) mevalonic acid (30), which yields isopentenyl pyrophosphate (31) and its isomer, 3,3-dimethyl ally pyrophosphate (32) a dimeric C -fragment, geranyl pyrophosphate (33), which gives rise to the iridoid loganin (34) and the trimer famesyl pyrophosphate (35), which is also considered the precursor to C q steroids, have already been mentioned (see Table 3... 

Another significant use of 3-methylphenol is in the production of herbicides and insecticides. 2-/ f2 -Butyl-5-methylphenol is converted to the dinitro acetate derivative, 2-/ f2 -butyl-5-methyl-4,6-dinitrophenyl acetate [2487-01 -6] which is used as both a pre- and postemergent herbicide to control broad leaf weeds (42). Carbamate derivatives of 3-methylphenol based compounds are used as insecticides. The condensation of 3-methylphenol with formaldehyde yields a curable phenoHc resin. Since 3-methylphenol is trifunctional with respect to its reaction with formaldehyde, it is possible to form a thermosetting resin by the reaction of a prepolymer with paraformaldehyde or other suitable formaldehyde sources. 3-Methylphenol is also used in the production of fragrances and flavors. It is reduced with hydrogen under nickel catalysis and the corresponding esters are used as synthetic musk (see Table 3). 

Tb allium acetate reacts with iodine and an alkene to give the /ra/ j -io do acetate derivatives in 90% yield (28) ... 

Ketal (Section 17.8) An acetal derived from a ketone. Keto-enol tautomerism (Section 18.4) Process by which an aldehyde or a ketone and its enol equilibrate ... 

The facile formation of cyclobutane products is indeed another important contribution of enamine chemistry (302-306). The formation of cyclobutanes has also been found in the closely related reactions of amino acetal derivatives of ketenes with acrylic esters (307). 

A crystalline 5,5 -diene, or bis (vinyl ether), derivative of sucrose has been prepared from 6,6 -dideoxy- 6,6 -diiodo-sucrose hexa-acetate, derived from the 6,6 -ditosylate, by treatment with silver fluoride in pyridine (26). 

This synthetic process is applicable to the preparation of other ketene acetal derivatives of /3-alkoxy alcohols. Examples include the ketene acetal derivatives of tetrahydrofurfuryl alcohol and l-methoxy-2-propanol.3 There are a number of advantages in its use, including a simple, time-saving procedure, readily available and inexpensive reagents, and good yields of ketene acetal obtained by a one-step method. 

The predominant formation of ann -carboxylic esters and thioesters results when the additives 13 or 14 are used to mediate aldol additions of silylketene acetals derived from propionates and propanethioates37. The enantioselective addition of a-unsubstituted esters or thioesters is also feasible with the borane 1437. 

The reaction of propargylic chiral acetals with a catalytic copper reagent (RMgX/5% CuX) provides the expected alkoxy allenes in quantitative yield (Table 3)61. The diastereomeric excess is highly dependent on the size of the ring of the acetal and on the type of substituents it contains. The best diastereomeric excess is 85% with the acetal derived from cyclooctanediol. The use of lithium dimethylcuprate results in 1,2-addition lo the triple bond and the resulting lithium alkenyl cuprate bearing a cyclic acetal does not eliminate even at reflux temperature ( + 35°C). 

Preparation of the acetate derivative Evaporate the extract to dryness. Add 50 fil of three parts acetic anhydride and two parts pyridine. Heat at 60° for 1 hour. Evaporate to dryness with clean, dry nitrogen and dissolve the residue in 25 ju.1 of ethyl acetate. 

GC separation of the acetate derivatives rhamnitol, fucitol. ribi-tol, arabinitol, mannitol, galacitol, glucitol, and inositol... 

Preparation of the acetate derivative Concentrate the aqueous mixture of saccharides to approximately 0.5 ml in a 20-50 ml container. Reduce the saccharides by adding 20 mg of sodium borohydride that has been dissolved carefully into 0.5 ml of water and let the reducing mixture stand at room temperature for at least 1 hour. Destroy the excess sodium borohydride by adding acetic acid until the gas evolution stops. Evaporate the solution to dryness with clean nitrogen. Add 10 ml of methanol and evaporate the solution to dryness. Acetylate with 0.5 ml (three parts acetic anhydride and two parts pyridine) overnight. Evaporate to a syrupy residue and add 1 ml of water. Evaporate again to dryness to remove the excess acetic anhydride. Dissolve the residue in 250 /d methylene chloride. 

Silyl enol ethers and ketene acetals derived from ketones, aldehydes, esters and lactones are converted into the corresponding o/i-unsaturated derivatives on treatment with allyl carbonates in high yields in the catalytic presence of the palladium-bis(diphenylphosphino)ethane complex (32). A phosphinc-free catalyst gives higher selectivity in certain cases, such as those involving ketene acetals. Nitrile solvents, such as acetonitrile, are essential for success. 

Selenoaldehydes 104, like thioaldehydes, have also been generated in situ from acetals and then directly trapped with dienes, thus offering a useful one-pot procedure for preparing cyclic seleno-compounds [103,104], The construction of a carbon-selenium double bond was achieved by reacting acetal derivatives with dimethylaluminum selenide (Equation 2.30). Cycloadditions of seleno aldehydes occur even at 0 °C. In these reactions, however, the carbon-selenium bond formed by the nucleophilic attack of the electronegative selenium atom in 105 to the aluminum-coordinated acetal carbon, may require a high reaction temperature [103], The cycloaddition with cyclopentadiene preferentially gave the kinetically favorable endo isomer. 

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