1.3- Diphenylisobenzofuran, preparation

Preparation. Potts and Elliott have reported an improved procedure for conversion of o-dibenzoylbenzene (1) into diphenylisobenzofurane (4). Reduction of (1) with excess sodium borohydride, followed by treatment with hot acetic anhydride, provides (4) in yields around 70%. Isolation of the intermediate alcohol (2) is not necessary. 

Arene oxides 42 and 49 were obtained as minor products by an unusual thermal isomerization of the photooxide of 3-diphenylisobenzofuran. Although the thermal isomerization reaction of 3-oxaquadricyclane has been used in the synthesis of benzene oxide 1, this route to benzene oxides was initially limited to specifically substituted derivatives owing to the unavailability of the unsubstituted 7-oxanorbornadiene. Thus most of the substituted arene oxides prepared by this route contained electron-withdrawing substituents X [X = —CF3 (77), —COaMe (76, 86, 88-92, 94), and —C02Et (93)] which increased their thermal stability. 

Efforts directed towards the synthesis of stable, perhaps isolable, cyclopropenyl anions having three identical anion stabilizing groups, such as cyano or benzoyl, have been attempted without much success. Tricyanocyclopropene (22a) could not be prepared except as a transient intermediate which could be trapped with diphenylisobenzofuran The corresponding triketone (22b) was obtainable, but attempted generation of the corresponding anion was thwarted by conjugate (Michael) addition of the base to the double bond. The cyclopropenyl anion remains an illusive species ... 

If the alkene is too unstable to permit isolation, it may be trapped in situ with a suitable reagent. The highly strained bridgehead alkene (40 Scheme 16) was prepared and trapped in this way as a Diels-Alder adduct with 1,3-diphenylisobenzofuran (41). ... 

The classical Hunsdiecker reaction was utilized in the laboratory of P.J. Chenier for the preparation of a highly strained cyclopropene, tricyclo[3.2.2.0 " ]non-2(4)-ene. The Diels-Alder cycloaddition was used to prepare the bicyclic 1,2-diacid, which surprisingly failed to undergo the Cristol-Firth modified Hunsdiecker reaction, most likely due to the unreactive nature of the diacid mercuric salt. However, the classical conditions proved to work better to afford the bicyclic 1,2-dibromide in modest yield. Treatment of this dibromide with f-BuLi generated the desired strained cyclopropene, which was trapped with diphenylisobenzofuran (DPIBF). 

Fluoride-ion promoted elimination of /J-halosilylcyclopropanes has also been utilized to prepare Diels-Alder adducts from less strained cyclopropene intermediates. Thus, when 1,1 -dibromo-2-trimethylsilylcyclopropane was reacted with potassium fluoride in diglyme containing 1,3-diphenylisobenzofuran, ( nc o-2-bromo-l,5-diphenyl-8-oxabenzo[/]bicyclo[3.2.1.0 ]octane (5) was obtained in 77% yield.Other examples can be found in refs 92,254, 347, 722, 728-737, 942. 

A less reactive bicyclo[3.2.0]hept-l(7)-ene substructure has been found in 164 (149). This compound was prepared from propellane 163 by photolysis and subsequent reduction. In contrast to 163, irradiation of the parent tricyclic ketone 165 in ethanol gives the saturated ketone 167. The formation of 167 is taken as evidence for the intermediate formation of the ketone 166. When 168 was treated with CsF in the presence of 1,3-diphenylisobenzofuran, an adduct was isolated, which was assigned the structure of the expected [2 + 4]cycloaddition product of 169 (150). 

Cycloaddition of diphenylisobenzofurans to (101), to sulphenes, to 2-phenyl-3-spirocyclopropylazirines, and to o-benzoquinonedi-imines have been reported. The preparation and trapping of 1-methoxy- and 1-benzyl-isobenzofuran have been described and a high degree of regio-and stereo-specificity is observed in the reactions of a range of 1-substituted isobenzofurans with quinone acetals, for example in the formation of... 

In contrast, 1,3-diphenylisobenzofuran 3 can be prepared from 3-phenyl-1,3-dihydroisobenzofuran-1-one 2 as follows ... 

Liberation of cyclobutadiene from its tetrahapto-iron tricarbonyl complex is believed to proceed via a dihapto iron complex, and the first such complex to be prepared by an independent method is [824 Fp — T -CpFe(CO)2]. On oxidation with iodide ion in the presence of diphenylisobenzofuran the adduct (825) of benzo-cyclobutadiene is obtained. A dinuclear complex with cyclobutadiene acting as a bridging ligand between two iron atoms has also been prepared. ... 

The intramolecular Diels-Alder cycloadditions of 1-aminobenzofurans provide a simple synthesis of benzo[/r]quinolines. A-Acetyl-2-azetine undergoes facile 4-1-2-cycloaddition with cyclopentadiene, 5,5-dimethoxy-1,2,3,4-tetrachlorocyclopentadiene, hexachloropentadiene, and diphenylisobenzofuran to produce exclusively endo-cyc o-adducts. The highly strained cyclic alkyne bicyclo[2.2.1]hept-2-en-5-yne (108), prepared from the heptavalent iodine precursor (107), has been trapped using 1,3-diphenylisobenzofuran to yield the adduct (109) (Scheme 41). The reaction of sodium dinitroxytrioxide (110) with 1,3-diphenylisobenzofuran gives an initial 4-1-2-cycloadduct (111), which rearranges to the final product (112) (Scheme 42). " The... 

In contrasL 1,3-diphenylisobenzofuran (3) is prepared from 3-phenylphthaHde (2) by addition of PhMgX or, in a more general synthesis [53], from (o-benzoyl)benzaldehyde (4) by chemoselective addition of PhMgX to the aldehyde function and subsequent acid-catalyzed dehydration ... 

We became interested in this area of chemistry because we wished to prepare some new and highly electrophilic 2//-azirines with potential for use as dienophiles in the Diels-Alder reaction. Vinyl azides appeared to be the most promising precursors. Previously there had been only one report of the cycloaddition of 2H-azirines to a simple diene (cyclopentadiene) although highly activated dienes such as tetraphenylcyclopentadie-none and 1,3-diphenylisobenzofuran had been used to intercept some transient 2H-azirines. Our investigations led to the preparation of several new 2ff-azirines. Cycloaddition reactions with these provided access to some novel fused-ring aziridines. An outline of the results is included in Sections 6.2 and 6.3. 

A -Dihydrothiopyrans (2) are produced by the action of Grignard reagents on diethylaminovinylthiones (1). The spectroscopic properties of the bicyclic compound (3) are not those of a typical vinyl sulphide the structure of its adduct with 1,3-diphenylisobenzofuran has been discussed. A new preparation of the diketone (4) has appeared."... 

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