vco 1710; NMR 1.15 (s, 9 ), 1.3-2.4 (m, 8 ), 4.05 (br m, 1 H), 4.8 (br m, NH); 19F NMR 155.5 (not resolved m).4,5-Tetramethylene-2-oxazolidone ( 19): DR: yNH 3450 (sharp), 3250 (br), i/co 1750; NMR 1.3-2.2 (m, 8 H), 4 (t, J = 4,1 H), 6.45 (s, 1 H), 7.46 (s, 5 H).JV-(tert-Butoxycarbonyl)-l-ethyl-7-azabicyclo[4.1.0]heptane (20d): crude product, IR t>co 1710; NMR 0.8-1.9 (m exhibiting a sharp s at 1.4, 22 H), 2,3 (m, 1 H). A 1-g (4.4 mmol) sample of 20d was allowed to react with NR3-2.5HF. The crude solid isolated (970 mg) exhibited only one signal in the 19F NMR spectrum; its NMR spectrum was consistent with pure 21dT. The structure of 21dT was confirmed by its hydrolysis to the amine 21aT in Olah's reagent, followed by Schotten-Baumann benzoylation to 24bT.JV-(tert-Butoxycarbonyl)-2-fluoro-2-ethylcyclohexylamine (21dT): yield 90; mp 107-109 °C (CH3CN); IR -3440, vCo 1710; NMR 0.9 (2 overlapping t,J= 7), 1.4 (s) and 1.2-2,2 (m, total 22 H), 3,85 (br m, 1 H), 4,7 (br m, 1 H); mass spectrum, mje