Endo Diels-Alder adduct

Conflicting results were reported for the reaction of 1,3-diphenylisobenzofuran with benzocyclopropene. Reaction in chloroform (207 days) reportedly gave the unsymmetrical 5,10-diphenyl-10,ll-dihydro-5,10-epoxy-5//-dibenzo[a,c/lcycloheptene (7) in 71% yield,which was derived from addition of the furan to one of the lateral cyclopropane bonds. However, under similar conditions, other authors also report the formation of the isomeric exo and endo Diels-Alder adducts 6 and 8 in low yield.Under optimum conditions (tetrahydrofuran, 80 °C, 3 days), the enr/o-adduct 6 was isolated in 52% yield.The formation of the unsymmetrical adduct 7 was ascribed to a radical reaction, similar to that observed in the addition of buta-1,3-diene to benzocyclopropene. 

Azirines bearing alkyl or aryl substituents apparently do not add to simple aliphatic 1,3-dienes. However, it has been reported that a benzoy-lazirine does combine rapidly with cyclopentadiene, affording an endo Diels-Alder adduct [Eq. (21)]. ... 

The effect of other Ln(OTf)3 was also examined. As shown in table 31, the choice of lanthanide element strongly influenced the yields and selectivities. A slight difference between the two catalyst systems (catalysts A and B) on the effect of the lanthanide elements was also observed. In catalyst A, lutetium triflate (Lu(OTf)3) was also effective in generating the endo Diels-Alder adduct in 93% ee. The yields and selectivities diminished rapidly in accordance with the enlargement of the ionic radii. In catalyst B, on the other hand, the best results were obtained when thulium triflate (Tm(OTf)3) or erbium triflate (Er(OTf)3) was employed. Deviations to either larger or smaller ionic... 

The regio- and stereo.selective 2 + 2 cycloaddition of phenylacetylene to the allene 147 results in the (Z)-cyclohutenylideneoxazolidin-2-one 148 similarly, methyl acrylate affords the analogue 149 <97JA10869>. The dimetliyleneoxazolidinone 150 adds methyl vinyl ketone in the presence of aluminium trichloride or titanium tetrachloride to yield mainly the endo Diels-Alder adduct 151 <97JOC4103>. 

Prolonged irradiation of the endo-Diels-Alder adduct formed between duroquinone and trnns,trans-hexa-2,4-diene yields the cage dione (930). Similar reaction of the exo-Diels-Alder adduct of quinone and diene, in which intramolecular allylic hydrogen abstraction by carbonyl oxygen or enone carbon is not impeded, results in the forma-... 

In addition to being stereospecific, there is a stereoselective preference favoring the formation of endo-Diels-Alder adducts from cyclic dienes as is evident in the observed 3 1... 

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