Esters benzyne reactions with

Isothiazoles are reported to yield the lactam (101) on reaction with diphenyl ketene <85BSB149>. Ethyne dicarboxylate esters add to 2,1-benzisothiazole to generate quinoline esters (102), and benzyne reacts to yield aeridine <83H(20)489, 88JCS(Pl)2l4l>. 2-Methyl-2,l-benzisothiazolin-3-thione with acetylene esters forms 2-iminobenzoquinone methides (103), which dimerize to give diazocines (104) or further react with the ethyne ester to yield diadducts (105). The initial adduct formed with phenylethyne and 2-methyl-2,l-benzisothiazolin-3-thione rearranges to produce l,2-dithiole[3,26]... 

Pyridyl esters 200 (R = COMe, COPh, COCF3) and nitrophenyl ethers react with benzyne to give 196.103 [Theether200(R = 2,4-dinitrophenyl) was for some time mistakenly believed to be the betaine, l-(2,4-dinitrophenyl)-pyridinium 3-oxide, and its reaction with benzyne was at first ascribed to the... 

Furan also undergoes cycloadditions with allenes," " with benzyne" and with simpler dienophiles, like acrylonitrile and acrylate various Lewis acidic catalysts can assist" in some cases, zinc iodide is one such, hafnium tetrachloride another, and improved endo exo ratios are obtained in an ionic liquid as reaction solvent. Maleate and fumarate esters react if the addition is conducted under high pressure. This device can also be used to increase markedly the reactivity of 2-methoxyfuran and 2-acetoxyfuran towards dienophiles. At higher reaction temperatures alkynes and even electron-rich alkenes will add to furan. 3- or 5-Halo-furans react faster in these cycloadditions. ... 

Like heptafulvene itself, its 8-cyano derivatives take part as an 8tt-component in [8+2]cyclo-addition reactions, for example with acetylenedicarboxylic esters [365] or with benzyne [368]. 

Reactions involving benzyne can be useful for formation of a carbon—carbon bond to a phenyl group (a process called phenylation). For example, if acetoacetic ester is treated with bromobenzene and two molar equivalents of sodium amide, phenylation of ethyl acetoacetate occurs. The overall reaction is as follows ... 

These reactions are found to be promoted by electron-donating substituents in the diene, and by electron-withdrawing substituents in the alkene, the dienophile. Reactions are normally poor with simple, unsubstituted alkenes thus butadiene (63) reacts with ethene only at 200° under pressure, and even then to the extent of but 18 %, compared with 100% yield with maleic anhydride (79) in benzene at 15°. Other common dienophiles include cyclohexadiene-l,4-dione (p-benzoquinone, 83), propenal (acrolein, 84), tetracyanoethene (85), benzyne (86, cf. p. 175), and also suitably substituted alkynes, e.g. diethyl butyne-l,4-dioate ( acetylenedicarboxylic ester , 87) ... 

The reaction of oxazoles with alkynes is entirely different, leading to furans. The adducts (157) eliminate a cyanide in a retro-Diels-Alder process (equation 15). A typical example is the formation of the ester (164) from 5-ethoxy-4-methyloxazole and dimethyl acety-lenedicarboxylate (equation 16) equation (17) illustrates the production of two regioisomers in this reaction (79MI41802) a more elaborate case is the twofold addition of benzyne to 4-methyl-2,5-diphenyloxazole to give the bridged dihydroanthracene shown in equation (18) (80TL3627). 

Attack at the heteroatoms was observed in the reactions of (1) and (2) with dimethyl acetylenedicarboxylate and with benzyne (78JCS(P1)1006). Compound (2) behaves as a heterodiene toward the acetylene ester, producing the quinoxaline (25) and selenium. The diester (25) was obtained only in trace amounts from (1). These reactions, and the failure of (1) and (2) to react with maleic anhydride, contrast with the behavior of naphtho[2,3-c] [l,2,5]thiadiazole which reacts with maleic anhydride across the center ring (64TL3815). 

Fascinating rearrangements of aziridines have been applied to the synthesis of diterpene alkaloids by Wiesner and co-workers (Scheme 40). For example, the ester 217, prepared from cyclopentadiene carboxylate (215) and the benzyne precursor 216 by a Diels-Alder reaction, was converted to the aziridine 218 by treatment with benzenesulfonyl azide in 83% yield. When the aziridine 218 was heated with water for 24 h, the hydroxy ester 219 was obtained in 97% yield subsequent oxidation with the Jones reagent afforded the ketone 220. This rearrangement is analogous to that of the benzenesulfonylaziridine of norbomene. ... 

Photolysis of bicyclo[3.2.2]octa-3,6-dien-2-one derivatives, for example the adduct of tropone with benzyne 33 a in water gave the three-membered ring derivative 35 a, while photolysis in acetonitrile gave the cyclopentanone derivative 37 a which must arise from the 1,3-shift product 36a.This different behavior in these two solvents was rationalized in the following way the efficient [3,3] shift of 33 a to cyclopropyl ketene 34 a is thermally reversible, so that in the absence of a nucleophile 35a is not observed. In that case, the less efficient 1,3-shift to form 36a and then 37a is the only detectable reaction. The ketene 34a was detected as the major product of photolysis of adduct 33 a at low temperature methanolysis of 34 a at — 80 "C gave only the enfifo-configurated ester 35 a. 

Naphthalene is formed from the N-nitrosoimine 69 at 45°C via a cheletropic reaction.62 In some instances benzyne induces deamination of naphthalen-l,4-imines, since naphthalene was a by-product of the reaction of benzyne with N-methylpyrrole,63 and the naphthalene ester 79 is produced by reaction of 78 with benzyne.68 An indication of the fate of the extruded nitrogen-containing fragment is provided by the identification of N-methylcarbazole as a product of the reaction of 82 with benzyne. 

Homoeyelic ring closures. Bunnett and Skorcz31 found that several aliphatic esters, nitriles, sulfones, and ketones bearing an m-o-chlorophenyl group react with potassium amide in liquid ammonia to form homocyclic products of ring closure by way of a benzyne intermediate. The procedure has since been modified to use sodium amide (commercially available).32 The reaction is probably the method of choice for synthesis of 1 -substituted benzcyclobutenes. 

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