A new norephedrine-derived chiral base for epoxide rearrangement reactions

Bimetallic Radical Redox-Relay Catalysis for the Isomerization of Epoxides to Allylic Alcohols

Organic radicals are generally short-lived intermediates with exceptionally high reactivity. Strategically, achieving synthetically useful transformations mediated by organic radicals requires both efficient initiation and selective termination events. Here, we report a new catalytic strategy, namely, bimetallic radical redox-relay, in the regio- and stereoselective rearrangement of epoxides to allylic alcohols. This approach exploits the rich redox chemistry of Ti and Co complexes and merges reductive epoxide ring opening (initiation) with hydrogen atom transfer (termination). Critically, upon effecting key bond-forming and -breaking events, Ti and Co catalysts undergo proton transfer/electron transfer with one another to achieve turnover, thus constituting a truly synergistic dual catalytic system.

Mechanistic insights for the transprotection of tertiary amines with Boc2O via charged carbamates: access to both enantiomers of 2-azanorbornane-3-exo-carboxylic acids

Development of a synthetic methodology for the selective transprotection in hindered tertiary amines using Boc₂O under N–C hydrogenolysis catalyzed by Pd/C: access to both enantiomers of 2-azanorbornane-3-exo-carboxylates.

A novel mixed dimer of a norephedrine-derived chiral lithium amide and 2-lithium-1-methylimidazole, and catalytic enantioselective deprotonation of cyclohexene oxide

Improved stereoselectivity has been obtained by using 2-lithium-1-methylimidazole, 2, as a replacement for lithium diisopropylamide (LDA) as a bulk base in catalytic deprotonations. The chiral lithium amide 6 of (1R,2S)-N-methyl-1-phenyl-2-pyrrolidinylpropanamine, 5, has been found to deprotonate cyclohexene oxide 3 in the presence of compound 2 to yield (S)-cyclohex-2-en-1-ol, 4, in 96% ee. Compound 2 is a carbenoid species conveniently generated from nBuLi and 1-methylimidazole, 1. The base 2 has also been found to play a more intimate role in the deprotonation. Investigations by 1H, 6Li and 13C NMR of the 6Li/15N isotopologue 8 of 6 have shown that 6 is homodimeric in THF and that, in the presence of 2, it forms a novel heterodimer 10. This heterodimer is found to be the dominant reagent in the initial state, rather than the homodimer of 6. Computational investigations with PM3 and B3LYP/6-311 + G(d,p) have shown possible structures of the heterodimers, as well as the role of THF and I in the solvation of the dimers. The results are in line with the NMR results. Favoured complexes in the equilibria between homo- and heterocomplexes are also reported.