Stereoselective alkylations of chiral nitro imine and nitro hydrazone dianions. Synthesis of enantiomerically enriched 3-substituted 1-nitrocyclohexenes.
Dianions of chiral nitro imines (generated by a combination of LDA and s-BuLi) underwent diastereoselective alkylation with methyl, butyl, isopropyl, allyl, and methallyl iodides. In contrast to the behavior of simple metalloenamines, the most selective auxiliary contained no coordinating groups but did possess a large steric difference between the two substituents. The yield and selectivity of the alkylations were improved by the addition of HMPA or DMPU. The use of (S)-1-naphthylethylamine as the auxiliary afforded the R absolute configuration of the alkylation products. This stereochemical outcome could be rationalized by simple steric approach controlled alkylation in a conformationally fixed, internally coordinated dianion. A SAMP nitro hydrazone gave poorer yields and selectivities.
Denmark
Scott E
SE
Roger Adams Laboratory, Department of Chemistry, University of Illinois, Urbana, Illinois 61801, USA. sdenmark@illinois.edu
Ares
Jeffrey J
JJ
D000478:Alkylation; D000838:Anions; D053138:Cyclohexenes / Q000737:chemistry*; D006835:Hydrazones / Q000138:chemical synthesis / Q000737:chemistry*; D007097:Imines / Q000138:chemical synthesis / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D009574:Nitro Compounds / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013237:Stereoisomerism
D000838:Anions; D053138:Cyclohexenes; D006835:Hydrazones; D007097:Imines; D009574:Nitro Compounds