1.3- Diacetoxy-5- benzene

Treatment of ethyl 1 W-azepine-l-carboxylate with palladium(II) acetate in benzene, or in an aprotic solvent, results in ring contraction (see Section 3.1.2.4.) or ring opening (vide infra), respectively, however, with palladium(II) acetate in acetic acid ethyl 2,3-diacetoxy-2,3-dihydro-l//-azepine-l-carboxylate (6) is formed as the major product along with ( , )-hexa-2,4-dienedial.243... 

The electrophilic addition of bromine to benzonorbornadiene was first reported by Wittig and Knauss to yield a dibromide (ref. 3). At about the same time, the related addition of bromine to a diacetoxy derivative (substituted in the benzene ring) of 1, which proceeded with rearrangement, was described (ref. 4). 

Methylene-1,4-pentadiene (83), prepared by flash vacuum pyrolysis of 1,5-diacetoxy-3-(acetoxymethyl)pentane, dimerizes at 95 °C in benzene to give predominantly one isomer of 1,4,4-trivinylcyclohexene (84) as the major product (equation 44)63. 

These important compounds are prepared either directly from iodoarenes and peroxyacids or through ligand exchange reactions. The first method is suitable mainly for diacetoxy-derivatives which are readily formed upon oxidation of iodoarenes with H202/Ac0H/Ac20. A detailed procedure for the parent (diace-toxyiodo)benzene can be found in Organic Syntheses (Scheme 4) [18]. 

The best known member among the various classes of these iodanes is undoubtedly [hydroxy(tosyloxy)iodo]benzene (HTIB), sometimes called Koser s reagent. It is prepared readily from (diacetoxyiodo)benzene and p-toluenesul-fonic acid monohydrate in acetonitrile. The same method using p-nitroben-zenesulfonic acid or 10-camphorsulfonic acid leads to the corresponding sul-fonyloxy analogs [41,42]. Of special interest are some iodanes of this type coming from a chiral ether. Their preparation was effected by direct oxidation with sodium perborate and the isolated diacetoxy derivatives were separately treated with p-toluenesulfonic acid in acetonitrile (Scheme 8) [43]. 

In a convenient experimental procedure, nitrogen heterocycles 3 are alkylated by a mixture of a carboxylic acid 4 and [bis(trifluoroacetoxy)iodo]benzene in boiling benzene or under irradiation in dichloromethane at room temperature (Scheme 2) [11, 12]. A similar procedure has been used for the stereoselective synthesis of C-nucleosides and their analogs via photolysis of the gulonic acid derivatives, (diacetoxy)iodobenzene, and the appropriate heteroaromatic bases [13]. 

Benzyne is an important reactive intermediate especially useful for the construction of polycyclic compounds via cycloaddition reactions with various dienes. Several benzyne precursors, including diphenyliodonium-2-carboxylate [ 1 ], have been previously used for the generation of benzyne by thermal decomposition. More recently, several new precursors that generate benzyne quantitatively under very mild conditions have been developed [105 -108]. An efficient benzyne precursor, iodonium triflate 109, can be readily prepared by the reaction of l,2-bis(trimethylsilyl)benzene 108 with [(diacetoxy)iodo]benzene in the presence of trifluoromethanesulfonic acid (Scheme 47) [105]. 

Palladium-catalysed directed C-H oxidation with (diacetoxy)iodobenzene of a series of meta -substituted aryl pyridine and aryl amide derivatives resulted in the formation of the corresponding acetoxy compounds. The reactions generally proceed with high levels of regioselectivity for functionalization of the less sterically hindered ortho-C-H bond.144 The mechanism shown in Scheme 4 has been proposed for the oxidation of 2,6-dimethylphenol with (diacetoxyiodo)benzene for the formation of 3,5,3, 5 -tetramethyl-biphenyl-4,4 -diol, via C-C coupling.145... 

Oxidative methanolysis of azetidinone 176 followed by hydrogenolysis of compound 177 afforded /3-lactam 178, which was protected to obtain the protected amine 179. The best conditions for rearrangement of 179 were found using TFA. Conversion of compound 180 to carbacephem 183 was accomplished by ketone reduction, alcohol protection, and elimination of methanol. Synthesis of carbacephem derivative 186 has been performed by rhodium(n)-catalyzed cycliza-tion of iodonium ylide 185 <1997TL6981> (Scheme 33). The iodonium ylide 185 was easily prepared from the corresponding /3-keto ester 184 and [(diacetoxy)iodo]benzene in good yield. 

With the exception of cyclic o-iodosylbenzoic acid (Section 12.1), unsubstituted iodosylbenzene is normally the reagent of choice. The best methods for its preparation involve hydrolysis of either (dichloroiodo)- or (diacetoxy-iodo)benzene. Both have been described but the latter is more convenient and has a better yield. 

The radical azidoselenenylation of alkenes can be achieved by reacting diphenyl diselenide with (diacetoxy)iodo-benzene in the presence of sodium azide. The unusual regiochemistry of this reaction is due to the radical... 

B. trans, trans-, A-Diacetoxy-, 3-butadiene. The diacetate above (83.0 g., 0.373 mole), dimethyl acetylenedicarboxylate2 (54.0 g., 0.380 mole), and benzene (250 ml.) are placed in a 500-ml. flask and boiled under reflux for 6 hours (Note 7). The solution is filtered to remove the remaining mercury and mercuric salts, and the benzene is distilled under reduced pressure. The residual viscous yellow oil is distilled under reduced pressure (Note 8). A mixture of l,4-diacetoxy-l,3-butadiene and dimethyl phthalate is collected at 140-155° (18-20 mm.), bath temperature 170-200°, from which the diene crystallizes as colorless needles in the cooled receiver. The solid in the receiver is broken up and washed onto a Buchner funnel with petroleum ether (b.p. 60-70°). The solid is then pressed between sheets of filter paper to remove excess dimethyl phthalate and recrystallized from acetone-petroleum ether (b.p. 60-70°) (ca. 1 2) (Note 9). The yield of colorless needles of trans,trans- 1,4-diacetoxy-1,3-butadiene, m.p. 102-104°, is 26-31 g. (41-49%) (Notes 10, 11, and 12). 

Diacetoxy-1,3-butadiene is a reactive diene in the Diels-Alder reaction. It has been used as the starting material in stereospecific syntheses of conduritol-D8 and shikimic acid,9,10 and in a simple general method of preparation of benzene derivatives, especially unsymmetrical biphenyls.11,12... 

Diniethylpiperazine-2,5-dione (34) on treatment with triethyloxonium fluoroborate in dichloromethane gave 5-ethoxy-l,3-dimethyl-2-oxo-l, 2,3.6-tetrahydropyrazine which was oxidized by DDQ in dry benzene to 5-ethoxy-l 3 dimethyl-2-oxo-l,2-dihydropyrazine (35) (1067). l,3,6-Trimethylpiperazine-2,5-dione similarly treated gave three products, one of which was assigned the structure 5-methoxy-l 3,6-trimethyl-2-oxo-l, 2-dihydropyrazine 3-benzyl-5-methoxy-l, 6-dimethyl-2-0X0-1,2-dihydropyrazine was also prepared similarly (1078). When 3,6-diethoxy-2,5"dimethyl-2,5-dihydropyrazine was refluxed with lead tetraacetate in dry benzene it gave a mixture of 2,5-diacetoxy-3,6-diethoxy-2,5-dimethyl-2,5-dihydropyrazine (36) (4 parts) and 2,5-diethoxy-3,6-dimethylpyrazine (1 part) (1068). 

Oxidation of 2,5-diethoxy-3,6-dihydropyrazine with dichlorodicyanobenzo-quinone (DDQ) formed 2,5-diethoxypyrazine (314), and the 3,6-dimethyl analogue reacted similarly (314). 2,5-Diisopropyl-3,6-dimethyl-2,5-dihydropyrazine was oxidized in alkaUne solution to 2,5-diisopropyl-3,6-dimethylpyrazine (225). Oxidation of 2,5-diethoxy-3,6-dimethyl-3,6-dihydropyrazine with lead tetraacetate in refluxing benzene gave both 2,5-diethoxy-3,6-dimethylpyrazine (minor product) and 2,5-diacetoxy-3,6-diethoxy-2,5-dimethyl-2,5-dihydropyrazine (1068). 

A solution of sulfur in dimethylformamide can act as an oxidant of certain A -blocked piperazine-2,5-dione derivatives, resulting in net dehydrogenation (1068). For example, (cis trans)-l,4-diacetyl-3,6-dibenzylpiperazine-2,5-dione (101) reacted with sulfur in dimethylformamide and triethylamine to form, after hydrolytic removal of the acetyl groups, 3-benzyl-6-benzylidenepiperazine-2,5-dione (102) (1968). Oxidation of 1,3,4,6-tetramethylpiperazine-2,5-dione (103) with lead tetraacetate in benzene gave 3,6-diacetoxy-3-acetoxymethyl-l,4,6-trimethylpiperazine-... 

Decalol, dehydration, 50, 92 Dewar benzene, 50,51 trans-1,8-Diacetoxybicyclo [4.2.0 ] octa-2,4-diene, 50,24 trans, [Pg.57]

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