STEREOCHEMICAL TESTS OF CYCLIC 1,1-DIALKYLDIAZENE FRAGMENTATION REACTIONS - THERMAL-DECOMPOSITION OF N-(CIS-NITRENES( AND TRANS-NITRENES) 2,3 AND 2,5-)DIMETHYLPYRROLIDINE)-NITRENES

The thermal decompositions of presumed 1, 1-diazenes, N-(cis-(and trans-)2, 5-dimethylpyrrolidine)nitrenes (30),generated from the base-induced decomposition of N-benzenesulfonamido-cis-(and trans-)2, 5-dimethyl pyrrolidines (28) inoctane (and diglyme) at 120 °C, afford propene, 1, 2-dimethylcyclobutanes, and l-hexene. The retention/inversion (r/i) ratiosof closure products are higher than those found from the corresponding 1, 2-diazenes in the gas phase at 306 and 439 °C. Thethermal decompositions of presumed 1.1-diazenes, N-(cis-(and trans-)2, 3-dimethylpyrrolidinc)nitrenes (31), generated fromthe base-induced decomposition of N-benzenesulfonamido-m-N-(cis-(and trans-)2, 3-dimelhylpyrrolidine (29) in octane (and diglyme) at ≤120 °C, afford 2-butenes and 1, 2-dimethylcyclobutanes. The stereospecificity in the 2-butanes and 1, 2-dimethylcyclobutanes is high. Analysis of the data indicates a 51% direct cleavage pathway to trans-2-butene and ethylene and 49%1, 4-biradical pathway from the decomposition of N-(trans-(2, 3-dimethylpyrrolidine)nitrene (trail.(trans-31). Similarly, N-(cis(2, 3-dimethylpyrrolidine)nitrene (cis-31) affords a 38% direct cleavage pathway to cis-2-butene and ethylene and 62% 1, 4-biradical pathway. Whether this stereospecific cleavage reaction is a concerted cycloreversion or results from a diazenyi biradical precursor cannot be distinguished from the data. The relative rates of rotation, cleavage, and closure for 3-methyl-1, 4-pen-tanediyl (35C and 35T) generated from the corresponding tetramethylene-1, 1-diazenes (31) in octane at ≤120 °C were determined. From 3SC, K (cleavage) /K(closure) = 1.6, k (closure)/K(rotation) = 4.9. From 35T, K(cleavage)/K(closure) = 4.7 and/c(closure)K:(rotation) = 3.1. Thermal decomposition of N-methanesulfonamido-cis-(and trans-)2, 3-(and 2, 5-)dimethylpyrrolidines (39 and 38, respectively) in the gas phase at 306 and 439 °C affords hydrocarbon products consistent with the inter-mediacy and subsequent decomposition of 1.1-diazenes (30 and 31). The retention/inversion ratios in the closure productssuggest that 1, 4 biradicals generated from cyclic 1, 1-dialkyldiazene decompositions in the gas phase at 306 and 439 ° behavemuch like those from cyclic 1, 2-diazene decompositions under similar conditions. 1, 4 biradicals with secondary radical centersgenerated from the same 1, 1-diazenes behave more stereospecifically in solution at lower temperatures (120 °C). © 1979, American Chemical Society. All rights reserved.