Unusually Facile Thermal Homodienyl‐[1,5]‐Hydrogen Shift Reactions in Photochemically Generated Vinyl Aziridines

Abstract

A range of photochemically generated tri- and tetracyclic vinyl aziridines have been found to undergo a general and surprisingly low temperature ring opening through a [1,5]-hydrogen shift reaction. The rate of the process was found to be highly dependent on the structure and substitution around the azirdine ring and the alkene terminus, with some substrates being observed to undergo ring opening at temperatures as low as 25 °C. The rigid nature of these polycyclic systems precludes a conformational explanation of these rate differences, and an Eyring study confirmed a negligible entropic barrier to the reaction. However, the Eyring plots for two different aziridines systems showed a significant difference in their enthalpies of activation. It is therefore believed that the levels of aziridine ring strain, as well as electronic effects, are the dominant factors in this sequence.

Rapid Access to Azabicyclo[3.3.1]nonanes by a Tandem Diverted Tsuji–Trost Process

“…With these conditions in hand, we explored the scope of this reaction (Figure 1), the substrates being easily accessible via a simple two‐step process from pyrrole 1 (R=CO 2 t Bu), involving photochemical conversion to tricyclic aziridine 7 followed by a one pot retro‐ene reaction/reductive amination sequence (see SI for details) [6a,c] …”

Using batch reactor results to calculate optimal flow rates for the scale-up of UV photochemical reactions

“…With this material in hand, our attention turned to the proposed homoerythrina alkaloid synthesis. A thermal retroene reaction 22 of aziridine 13 yielded imine 16, which was subsequently reduced to amine 17. Deprotection and activation of the alcohol was performed in a single step and telescoped with the cyclisation, leading to the formation of tricycle 14 in up to 24% yield and 5.6 g scale from δvalerolactone over 6 steps (Scheme 5).…”

Conformationally Driven Two- and Three-Photon Cascade Processes in the Stereoselective Photorearrangement of Pyrroles

“…9, 12 As the stereogenic centre bearing the OTBS group had such a profound and consistent level of stereocontrol during rearrangement, we were keen to prove that an asymmetric synthesis of 11 could be achieved in high e.e. from enantiopure 10.…”