Acetoxy group, elimination

In order to deprotect the acetates, KCN in MeOH was chosen as a mild method to effect transesterification. Since the NMR spectra corresponding to authentic samples of the natural products were obtained in CD3OD and since methanol was the reaction solvent, the transformation was performed in an NMR tube and followed by NMR. Surprisingly, the transesterification reaction did not take place at all, and instead, the C6 acetoxy group eliminated selectively to provide myriaporone 1 exclusively. The identical reaction occurred when applied to both C5 diastereomers. 

Also obtained by reaction of 3-acetoxy-a-bromoacetophenone (m.p. 71-72°) with hexamethylenetetramine in chloroform, followed by acetoxy group elimination in the obtained compound with hydrochloric acid [4721]. 

Vinyl acetate reacts with the alkenyl triflate 65 at the /3-carbon to give the 1-acetoxy-1,3-diene 66[68]. However, the reaction of vinyl acetate with 5-iodo-pyrimidine affords 5-vinylpyrimidine with elimination of the acetoxy group[69]. Also stilbene (67) was obtained by the reaction of an excess of vinyl acetate with iodobenzene when interlamellar montmorillonite ethylsilyl-diphenylphosphine (L) palladium chloride was used as an active catalyst[70]. Commonly used PdCl2(Ph3P)2 does not give stilbene. 

The 10l -acetoxy group can be red actively removed with zinc and acetic acid or chromous chloride to give I9-norsteroids in high yield. Thermal elimination (boiling tetralin) of acetic acid from the crude 10)5-acetoxy-A -3-ketone or treatment with methanolic alkali leads to aromatization of ring A. Estrone alkyl ethers are formed from 10)5-acetoxy-19-nor-A -androstene-3,17-dione by treatment with alcohols and perchloric acid. Similar aromatizations are observed with 5,10-oxido, 5,10-dihydroxy, 5,10-halohydrins or 5,10-dihalo-3-ketones. ... 

Substituted furan formation by an indirect cyclization of 1,4-dicarbonyl derivatives has also been adopted as a key step in the synthesis of 3-oxa-guaianolides. Although 1,4-dicarbonyl compounds have been traditionally considered as the direct precursors for furans, treatment of 1,4-dicarbonyl compounds having a tertiary acetoxy group with p-toluenesulfonic acid leads to only 11% yield of an alkenylfurans as derived from a cyclization/acetoxy-elimination route. The following scheme shows an alternative multi-step conversion of the 1,4-dicarbonyl that leads to a more acceptable yield of the acetoxyfuran . 

A two-step sequence to prepare di-O-acetyl-3-deoxy-D-arabino-l, 4-lactone from tri-O-acetyl-D-ribono-1,4-lactone has also been reported, but in a low yield of 46% because ol the difficulty of controlling the elimination of the 3-acetoxy group, since the 2,3-unsaturated lactone also undergoes further elimination.5 Furthermore, partial racemization of the enolizable 2,3-unsaturated lactone could occur during treatment with DBU.6... 

The acetoxy group of 9-(l-acetoxyethyl)carbazole is easily displaced with alcohols. Easy displacement of a similarly situated halogen can be achieved, as has been noted before (see Section II,C,2) thus methanol converts 9-(l-chloro-2-iodoethyl)carbazole to 9-(2-iodo-l-methoxyethyI) car-bazole. Elimination of acetic acid or ethanol by strongly heating 9-(l-acetoxyalkyl)- or 9-(l-ethoxyalkyl)carbazoles gives 9-vinylcarbazoles. In the absence of acid, ( )-alkenes are produced, but acid catalysis leads to a mixture of E and Z isomers. Acetyl chloride in pyridine also effects ethanol elimination. ... 

Aliphatic aldehydes react to form monoalkylidene derivatives only in presence of potassium r-butoxide. A mechanism has been postulated that also explains the observed N-deacetylation during the formation of the product. The essential step in this is the intramolecular N - O acetyl migration in the initially formed aldol. Subsequent protonation and elimination of the acetoxy group lead to the product (Scheme 26). 

Essentially the same substituents as listed above may be present in the alkene being substituted, with the possible exception of chloro, alkoxy and acetoxy groups on vinyl or allyl carbons. These groups, especially chloro, may be lost or partially lost with palladium when the final elimination step occurs. For example, vinyl acetate, iodobenzene and triethylamine with a palladium acetate-triphenylphosphine catalyst at 100 C form mainly (E)-stilbene, presumably via phenylation of styrene formed in the first arylation step (equation 21 ).6 ... 

Upon addition of boron trifluoride etherate, acetoxylactam 8 eliminates an acetoxy group to produce A-acyliminium ion 9. The indo-lizidinone 10 is formed diastereomerically pure in an iminium-ion-ini bated cyclization reaction of the Overman type ending in a vinyl-silane.14... 

When 2-hydroxypyrazole 1-oxide 106, possessing a substituent at the 4-position, is reacted with acetic anhydride the acetoxy compound 219 is formed and can be isolated (1974JOC2663). Presumably, acetylation of the OH group of 106 is followed by nucleophilic addition of the liberated acetate ions followed by elimination of acetic acid. By heating 219 in diox-ane solution, the acetoxy group migrates to the 4-position giving rise to 220 (Scheme 63). 

The acetoxy group may also be substituted using N-nucleophiles such as pyrrolidine or morpholine. Since the products of nucleophilic substitution are aminals, elimination results in /3-substituted ethane sulfonamides 108. Moreover, while no reaction occurs with phthalimide or sodium azide, trimethylsilyl azide reacts in the presence of Lewis acids such as zinc chloride or tin chloride to give a diazido compound 109 as product (Scheme 32) <1997PHA482>. 

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