Front Cover: Reductive Rearrangement of a 1‐Phospha‐2‐azanorbornene (Chem. Eur. J. 29/2021)

Abstract

When fed the right food, the hermit crab depicted in the cover image grows bigger and finally needs a larger shell. This work reports the reactivity of a 1‐phospha‐2‐azanorbornene, the product of a hetero Diels‐Alder reaction between a 2H‐phosphole and an activated imine. Thus, reductive cleavage of the phosphorus−nitrogen bond with LiAlH4 leads to an unprecedented ring expansion with formation of a 1‐phosphabicyclo[3.2.1]octa‐2,5‐diene. The cover image was designed by Dr. Christoph Selg. More information can be found in the Full Paper by E. Hey‐Hawkins et al. (DOI: 10.1002/chem.202100898).

Facile Synthesis of Enantiomerically Pure P‐Chiral 1‐Alkoxy‐2,3‐dihydrophospholes via Nucleophilic P‐N Bond Cleavage of a 1‐Phospha‐2‐azanorbornene

“…[16] The straightforward preparation of PANs and their reactive PÀ N bond allow numerous derivatizations and therefore access to P-stereogenic compounds with multiple stereocenters. While reduction of the diastereomerically pure endo-5-phenyl-1-phospha-2-azanorbornene (R P /S P )-endo-1 with lithium aluminum hydride (LAH) yielded a seven-membered P-heterocycle, [17] the PÀ N bond could also be cleaved by achiral nucleophiles (H 2 O, H 2 S, EtMgBr) to give 2,3-dihydrophosphole derivatives as a racemic mixture. [13d] We here report the facile one-pot synthesis of enantiomerically and diastereomerically pure 1-alkoxy-2,3-dihydrophosphole derivatives obtained via PÀ N bond cleavage of diastereomerically pure endo-5-phenyl-1-phospha-2-azanorbornene (R P /S P )-endo-1 (Scheme 3).…”

“…The straightforward preparation of PANs and their reactive P−N bond allow numerous derivatizations and therefore access to P ‐stereogenic compounds with multiple stereocenters. While reduction of the diastereomerically pure endo ‐5‐phenyl‐1‐phospha‐2‐azanorbornene ( R P / S P )‐ endo ‐ 1 with lithium aluminum hydride (LAH) yielded a seven‐membered P‐heterocycle, [17] the P−N bond could also be cleaved by achiral nucleophiles (H 2 O, H 2 S, EtMgBr) to give 2,3‐dihydrophosphole derivatives as a racemic mixture [13d] …”