Solution and Solid Phase Synthesis of Unusual a-Amino Acids From

67.1 (Ar_cH20), 63.2 @--a),
56.3 (am, 39.5 (oxetane ester CCH3), 20.7 (oxetane
ester C-3); IR (cast fiom CHZC12) 3371, 3û64, 3034, 2956, 2879, 1723, 1525, 1457,
1339, 1214, 1195, 1061; Anal. cdcd. for CI&12106N: C, 59.43; H, 6.55; N, 4.33. Found:
C, 59.44; H, 6.61; N, 4.31.
3.42 1-[N-(Be~loxy~nyI)-(1S)-1-amin012lethan01]4methyI-2,6,7-trioxa-
bicyclo[2.2.2]octane, Cbz-L-Ser-OBO ester, 3.41.
Cbz-Ser oxetane ester 3.40 (15.0 g, 46.2 mrnol) was dissolved in dry CHtC12 (450 mL)
and cooled to O°C under Ar. BF3- Et20 (O. 1 1 mL, 0.93 mrnol) was diluted in CH2C12 (5.0
mL) and added to the reaction flask after which the reaction was allowed to wann up to
room temperature. After 6 hours, Et3N (1.29 rnL, 9.25 mol) was added and the reaction
stirred an additional 30 minutes before king concentrated to a thick oil. The crude
product was redissolved in EtOAc (400 mL) and washed with 3% -1 (2 x 250 d),
10% NaHC03 (100 mi,), saturated NaCl (250 mL), dned (MgS04), and evaporated to
Mess. The reaction yielded a colourless thick oil in 95% (14.2 g) yield which was
crystallized from Et0Ac:Hexanes to give rd-like shiny crystds in 93% (13.6 g) yield.
mp 103.5-105.0 OC; [al2OD = -24.8 (c = 1.00, EtOAc); TU3 (3: 1 EtOAc:Hex), Rr = 0.37;
'H NMR (CDCls, 250 MHz) 6 7.36-7.31 (m, 5H, ArH). 5.34 (br d, lH, J = 8.8Hz, NH),
5.17-5.1 1 (m, 2H, CbzCHfl), 3.94-3.83 (m. ZH, a-CH, p-CHH), 3.9 1 (s, 6H, OB0 ester