Synthesis of a Congested Heptamine as a Potential Precursor to Hypervalent (10-n-5) Nitrogen, and Effects of Remote Substituents on Planarization of Nitrogen in Trialkylamines

Abstract

The challenging synthesis of a congested heptamine 10, as a potential precursor to hypervalent (10-N-5) nitrogen, was pursued by employing four different strategies. Even though these strategies didn’t lead to a successful synthesis of 10, strategy 4 seems more likely the way forward if deprotection of a single acetonide group of 105 is possible in the future. Investigation into the unprecedented formation of ester-amides 85 and 87 in Rh2(OAc)4 catalyzed N-H insertion with dimethyl diazomalonate 19 led to the identification of other minor side products 88, 89, 90 and 91. The 1:1 ratio of ester-amides 85/87 with 88 led us to propose a mechanism that involves a novel thermal intermolecular Wolff rearrangement. Analysis of planar and nearly planar trialkylamines 20, 85, 86, 87 and 105, gave anomalies that could not only be explained by steric congestion around nitrogen as it is in the case of triisopropylamine. Planarization of these trialkylamines can be explained by a simple p-* hyperconjugation argument. Hyperconjugation was also supported through computational methods i.e. Natural Bond Orbital analysis.