Reactive Intermediates fromN-Aziridinylimines

Abstract

N‐Aziridinylimines are readily obtained from carbonyl compounds and 1‐aminoaziridines, of which the 2‐phenyl and trans‐2,3‐diphenylaziridine derivatives are the most popular. Diazo compounds are formed upon thermolysis or photolysis of N‐aziridinylimines, with elimination of alkenes. The diazo compounds can be trapped by intramolecular addition to alkenes, but otherwise decompose as they are formed, giving rise to carbenes and products derived therefrom. The transformation R2CO → R2CN2 → R2C is most often achieved with the anions (salts) of arenesulfonylhydrazones. However, the non‐ionic and weakly basic N‐aziridinylimines have the advantage that they are compatible with nonpolar solvents and with a wide range of substituents. These properties were exploited in the fragmentations of α,β‐epoxyketones (→ alkynones) and α,β‐epoxyaldehydes (→ β‐hydroxyvinylidenes → cyclopentenols) as well as in the syntheses of unsaturated nitriles, silanes, and ethers. Laser flash photolysis of N‐aziridinylimines in fluorinated alcohols was used to demonstrate the protonation of carbenes and to measure absolute reaction rates of carbocations. The Shapiro reaction of N‐aziridinylimines, performed with catalytic amounts of R2NLi, was found to produce alkenes with excellent regio‐ and stereoselectivity. As radical acceptors, N‐aziridinylimines are superior to alkenes. On this basis, selective (tandem) cyclizations were designed for the synthesis of natural products.

Recent advances in alkylidene carbene chemistry

“…The thermal decomposition of a,b-epoxy-N-aziridinylimines 40 allows for the generation of alkylidene carbenes under neutral conditions. 33 This approach also offers an additional benefit, allowing for the generation of an alkylidene carbene with a b-hydroxyl group. The decomposition is thought to proceed in a similar fashion to the Eschenmoser fragmentation.…”

N,N-Dialkylhydrazones in Organic Synthesis. From Simple N,N-Dimethylhydrazones to Supported Chiral Auxiliaries

“…39 A special family of hydrazones, the N-aziridinylimines, known as Eschenmoser hydrazones, can be prepared by direct reaction of 1-aminoaziridines (1-amino-2-phenylaziridine and 1-amino-trans-2,3-diphenylaziridine) with reactive carbonyl compounds at temperatures below 40°C or with imines (substitutes for less reactive carbonyl compounds). 24,40 Cleavage of the N,N-dialkylhydrazones (Scheme 2) can be effected by a multitude of methods. 41 Methods for recovery of carbonyl compounds from N,N-dimethyl-and SAMP/RAMP-hydrazones were thoroughly reviewed in the Enders' account.…”

Direct Access to Tetrahydro[1,2]diazepinones from α,β-Epoxy-N-aziridinylimines via Anionic Rearrangement

“…For instance, these compounds have been employed as the precursors of many reactive intermediates such as diazoalkanes, carbenes, and carbocations. 1 In addition, N-aziridinylimines have been used in a catalytic Shapiro reaction 2 and to produce geminal methylene radicals 3aÀe and trimethylenemethane (TMM) biradical intermediates, 3f to effect further radical cyclizations. The TMM biradical chemistry resulted in facile construction of triquinanes and was applied to an elegant total synthesis of hirsutene.…”

“…9 During the course of our investigations related to the Shapiro reaction, we discovered that, upon treatment with 1.5 equiv of MeLi, n-BuLi, or lithium diisopropylamide (LDA) at À78 °C, 2a underwent an unprecedented rearrangement to afford 3a in a good to excellent yield (entries 6À8, Table 1). Compound 3a features a novel and potentially biologically significant 10 1,5,6,7-tetrahydro [1,2]diazepin-4-one core structure. n-BuLi and LDA seemed to be slightly better than MeLi as the base since they led to higher yields of the product.…”