Reductive Rearrangement of a 1‐Phospha‐2‐azanorbornene

Abstract

The reduction of the 1-phospha-2-azanorbornene derivate endo-1 with lithium aluminium hydride leads to an unprecedented 1-phosphabicyclo[3.2.1]octa-2,5-diene, while a phospholide anion is formed with lithium. The latter can be protonated resulting in formation of an unusual 2H-phosphole dimer. Furthermore, 3H-phospholes, previously assumed to have no synthetic relevance as intermediates, were proposed to act as dienophile in the dimerisation of 3,4dimethyl-1-phenylphosphole at elevated temperatures based on theoretical calculations.

Access to Enantiomerically Pure P-Chiral 1-Phosphanorbornane Silyl Ethers

“…We also showed that the reactive P-N bond of PANs can be cleaved by both achiral and enantiopure nucleophiles to yield racemic 2,3-dihydrophosphole and optically pure 1-alkoxy-2,3-dihydrophosphole derivatives, respectively [40,41]. Moreover, the reduction of PAN with lithium aluminum hydride (LAH) resulted in a seven-membered P-heterocycle [42]. Previously, we reported the first stereoselective HDA reaction between (5R)-(L-menthyloxy)-2(5H)-furanone (MOxF) and 2H-phospholes (Scheme 1) to produce P-chiral 1-phosphanorbornenes (2) [43] as well as P-chiral 7-phosphanorbornenes [44] in high yields.…”

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

“…The use of activated imines as dienophiles in an aza‐Diels‐Alder reaction proved to be a powerful method to produce heterocyclic compounds with feasible control over stereoselectivity as well as regioselectivity [14] . Based on this approach, we reported the first chemo‐ and regioselective phospha‐aza‐Diels‐Alder reaction between 2 H ‐phospholes and an N ‐sulfonyl α‐imino ester to afford diastereomers of 1‐phospha‐2‐azanorbornenes (PANs) as racemates (Supporting Information, Section 1.1) [13d] . The nature of the phosphorus‐nitrogen single bond has been extensively studied, [15] and a plethora of publications have been reported on P−N bond cleavage since the 1960s [16] .…”

“…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] …”

Synthesis of P-stereogenic 1-phosphanorbornane-derived phosphine–phosphite ligands and application in asymmetric catalysis

“…Hey-Hawkins and co-workers reported the first phospha-aza-Diels–Alder cycloaddition reactions to give P *-phosphacycles (1-phospha-2-azanorbornenes) 26 and could show that the products undergo P–N bond cleavage to afford racemic and enantiopure 1-alkoxy-2,3-dihydrophosphole derivatives 27,28 or reduction to seven-membered phosphacycles. 29 Moreover, in 2012 we reported an unprecedented asymmetric phospha-Diels–Alder reaction between 2 H -phosphole and (5 R )-( l -menthyloxy)-2(5 H )-furanone (MOxF) to give P -stereogenic 1-phosphanorbornenes in high diastereoselectivity (Scheme 1). 26 The diastereomers were separated via crystallization.…”