Liebigs Annalen p. 1611 - 1618 (1997)
Update date:2022-07-30
Topics:
Abdel-Wahab, Abdel-Magd A.
Ismail, Mohamed T.
Mohamed, Omima S.
Duerr, Heinz
Ma, Yinmin
The chemistry of 4,5-diazafluorenylidene (3), generated from the diazo compound 3a by photolysis, has been studied with regard to reactivity, multiplicity and selectivity. Reaction of 3 in 2,3-dimethylbutene gave exclusively ketazine 24. The [1 + 2] cycloaddition with styrenes 5-11 afforded cyclopropanes 16-23 in 25-54% yields and 24 as a side product. In these reactions no diazirine intermediate was involved. Irradiation of 3a in methanol afforded the ether 26 (25% yield). The stereoselectivity of 3 was studied by its addition to (E)- and (Z)-β-methylstyrene. A mixture of the (E)- and (Z)-cyclopropanes 22 and 23, respectively, was detected. Thus for 3, triplet multiplicity was concluded. The results of competition experiments with singlet/triplet scavengers (methanol/dimethylbutadiene) demonstrated that an equilibrium between singlet and triplet manifold of 3 exists at room temperature. Selectivity studies with carbene 3 were carried out by evaluating the competition experiments of the cycloaddition of 3 with differently substituted styrenes. A plot of the krel values from the competition studies versus Hammett ω constants gave ρ = -0.65 indicating that carbene 3 reacts as an electrophile. VCH Verlagsgesellschaft mbH, 1997.
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