1.3- Diphenylisobenzofuran, reaction

The cyclopropenes were distilled directly from the reaction mixture and were characterized by trapping as Diels-Alder adducts with 1,3-diphenylisobenzofuran (X = Br, 77%, mp 107-109"C X = Cl, 54%, mp 104-106 C). The same method was used to generate the unstable 7-chlorobicyclo[4.1.0]hept-l(7)-ene which was trapped in situ by 1,3-diphenylisobenzofuran. Reaction of the silanes 2 with tetrabutylammonium fluoride in tetrahydrofuran gave 1,2-dibromocyclopropene (3a) or 1-bromo-2-chlorocyclopropene (3b) ... 

Cava and Schlessinger have reported the synthesis of 1,2,3-triphenyl-isoindole (65) in 78% yield from 1,3-diphenylisobenzofuran (68) hy reaction with thionylaniline (69) and boron trifluoride. The mechanism proposed for this remarkable transformation involves reaiTangement of the adduct (70) derived from thionylaniline and the isobenzofuran, to the tricyclic intermediate (71). This presumably collapses to the S-sultam (72), which yields the isoindole (65) upon extrusion of sulfur dioxide. Loss of sulfur dioxide, both from S-sultones and unsaturated S-sultams, is well documented. ... 

Scheme 6.90 Products of the reactions ofthe cyclic allene 417 with furan, 1,3-diphenylisobenzofuran and pyrrole.

One of the drawbacks associated with the cycloadditions based on 27 is the low reactivity of halogenocyclopropenes towards dienes. This may be overcome if furans or isobenzofurans are used instead. The aromatization of the adducts is, however, not straightforward. For example, reaction of the exo-a.dd iCt of 27 to diphenylisobenzofuran (DPHIBF, 44) with BuLi affords no cycloproparene, but a product 46, where the bromo substituent is replaced by hydrogen. Aromatization may, however, be effected by use of low-valent titanium. This sequence provides a simple access to 48. The parent 42 is also available by this route from 45 via 47. Exposure of adducts of furans, such as 49, to low-valent titanium leads, however, to mixtures of benzocyclopropehe (1) and 1,6-dihalogenocycloheptatriene (51). Cycloaddition of furans to tetrahalogenocyclopropenes may equally be realized, but the adducts decompose in the presence of low-valent titanium and afford no cydoproparenes. 

Diphenylisobenzofuran (DPIBF, 44) or furan have been used to intercept cyclopropa[fl]naphthalene (56) and cyclopropa[/]phenanthrene (142). ° ° DPIBF (44) reacts with 1 in THF at 20 °C to form exo and endo adducts 321 and 322 217 unsymmetrical adduct 323, resulting from ring-opening of 1, may also be obtained if the reaction is carried out in CHCl, in particular at higher temperatures." " ... 

The strain of the triple bonds of 5 could also be reflected by its chemical reactivity with furan, 1,3-diphenylisobenzofuran, as well as dichloroketene (Scheme 3). Mention should be made of my first use of furans in a Diels-Alder reaction, because this first encounter has sparked my enduring interest in furan chemistry throughout my research career (Section 6). 

There are photocalorimetric enthalpy data for two other ozonides, both coming from sensitized photochemical dioxygenation reactions in non-polar solvents . This study reports the enthalpies of the reactions of 2,5-dimethylfuran and 1,3-diphenylisobenzofuran to their corresponding endoperoxides to be exothermic by —45 20 and —92 25 kJmoU (the latter value is an average of the values given for different solvents). From... 

Since the seminal work of Bartlett [363] there have been relatively few reports of useful cycloadditions of fluoroalkenes. Recent work by Haufe showed that fluorine atom substituents depress the reactivity of styrene derivatives in the Diels-Alder reaction with 1,3-diphenylisobenzofuran. A single fluorine atom in the /1-position lowered the rate of the [4 + 2] reaction by a factor of ten when the fluorine atom occupied the -position (Eq. 142), the reaction was over 30 times slower than that of the unsubstituted styrene. 

Density functional theory computational studies have been used to determine die importance of secondary orbital interactions for the stability of transition-state structures for die 4 + 2-cycloaddition of furan with cyclopropene.175 Kinetic studies of die 2 + 4-cycloaddition of 2-cyclopropylidene acetates with furan and dimethylful-vene suggest a mechanism involving diradicals or zwitterions as intermediates.176 Cyclopropene, produced by die reaction of allyl chloride with sodium bis(bimediyl-silyl)amide, reacts with 1,3-diphenylisobenzofuran to produce both endo- and exo-Diels-Alder cycloadducts isolated for the first tune.177... 

Reactions with dienes and carbonyl compounds did either not occur below 150°C (e.g. 2,3-dimethylbutadiene, cyclopentadiene, tetrachloro-a-pyron acetaldehyde), or were accompanied by decomposition (2,3-dicarbomethoxybutadiene, hexachlorocyclopentadiene, 1,3-diphenylisobenzofuran acrolein ). However, 1,3-dipoles reacted readily to give well-defined addition products ... 

That 1,2-cyclohexadiene (161, n = 3) is formed in a related system, from the reaction of 1-bromocyclohexene with potassium t-butoxide in dimethyl sulphoxide, is shown by trapping it by the highly reactive 1,3-diphenylisobenzofuran (162). The Diels-Alder adduct (163), differs from that of cyclohexyne (164) which was obtained from 1,2-dibromo-cyclohexene and Mg in the presence of (162). The product (164) did not isomerize to (163) (Wittig and Fritze, 1966). 

The reaction of 1,3-diphenylisobenzofuran with cyclopropanone was studied in detail <95JOC4395>. 

The Diels-Alder addition of cyclopentadiene to iV-acetyl-2-azetine 23 occurs by single crystal X-ray analysis of the />-nitrobenzenesulfonamide 24 (R = 4-02NC6H4SC>2). X-Ray studies of crystals of adducts 25 (R = OMe and R = C1) obtained by reaction of 23 with 26 (R = OMe and R = C1) showed that these products were also formed by endo-addition. Similarly, the reaction of diphenylisobenzofuran with azetine 23 also gave the endo-adduct <1999TL443>. 

The intermolecular [4+2] cycloaddition of cyclopentadiene and iV-acetyl-2-azetine 23 occurs when they are heated in toluene in a sealed tube to give a good yield (83%) of the Diels-Alder adduct 317 (Equation 35). Similar high-yielding addition reactions occur with substituted cyclopentadienes and 1,3-diphenylisobenzofuran to give endo-adducts <1999TL443>. 

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