Macrocyclization of alpha-(alkynyloxy)silyl-alpha-diazoacetates by inter-/intramolecular [3+2] cycloaddition reaction sequences

Thermally induced intra-/intermolecular [3 + 2] cycloaddition reaction sequ ences of alpha-(alkynyloxy)silyl-alpha-diazoacetates 1 lead to [3.3](1,4)py razolophanes (2)(2) and higher cyclooligomers thereof [(2)(n), n > 2]. In m ost cases, the cyclodimer was isolated by crystallization, while a complete separation of the mixture of the higher cyclooligomers was not possible. S olid state structures of cyclodimers (2b)(2) and (2c)(2), cyclotrimer (2b)( 3), and cyclotetramer (2e)(4) were determined by X-ray diffraction analysis . Field-desorption mass spectra were used to characterize the cyclooligomer mixtures. The relative amounts of the cyclooligomers depend on the substit ution pattern of the diazo compound. The cyclooligomerization reactions rep orted herein demonstrate, for the first time, the involvement of diazo func tions in macrocyclization reactions via 1,3-dipolar cycloaddition.