Sterically Congested Molecules, 17. – Novel Syntheses of α,α,β‐Tri‐tert‐butyl Compounds

Pivaloin (2), prepared from ethyl pivalate (1) or from dimethyl oxalate (3), reacts with tert-butyllithium by reduction (45% of 10) and addition (45% of 9), whereas the corresponding Barbier variant takes a different course. Productive transformations of the α,α,β-tri-tert-butyl glycol 9 lead to α,β,β-tri-tert-butylethanone (17, overall 4 steps), or α,α,β-tri-tert-butylethene (20, 3 or 4 steps), or α,β,β-tri-tert-butyl-β-hydroxyethanone (19, 3 steps, also by Grignard addition to bipivaloyl 4). Steric congestion is assessed by searches for restricted internal rotation. The alkene 20 and its epoxide 27 are studied with respect to NMR assignments and chemical degradation.