1 -Methyl-2,6,7-trioxabicyclo -heptan

The checkers also prepared racemic 1-[N-benzyloxycarbonyl-(1 )-1-amino-2-hydroxyethyl]-4-methyl-2,6,7-trioxabicyclo[2.2.2]octane using the identical procedure (50% over 2 steps from racemic Cbz-serine purchased from Aldrich Chemical Company, Inc.). The enantiomeric ratio of the crystalline (S)-3 enantiomer (Note 20) was > 99.5 0.5 as determined by comparison with racemic 3 by courtesy of Mr. Eric Hortense (GlaxoSmithKline, Stevenage). Chiral HPLC (25 cm Chlracel OD-H, Column No ODHOCE-IF029, mobile phase ethanol/heptane 1 4 v/v, UV detector at 215 nm, flow rate... 

Polymerization of 80 at — 78 °C gave a polymer consisting mostly of five-membered rings (81), which indicates that dominant cleavage takes place at the C(l)—0(2) bond. [81] l-Methyl-2,6,7-trioxabicyclo[2.2.2]heptane also gave a polymer, which was found to consist of five membered rings from 13C NMR spectra, contrary to an earlier report. [83]... 

Ethyl 3,3-diisopropyl-7-erccfo- and -7-e.To-methyl-2,4,6-trioxabicyclo[3.2.0]heptane-7-carboxylate22 is obtained from ethyl pyruvate and 2,2-diisopropyl-l,3-dioxole, ratio 7-CH3 endo/exo 4 1. The isomers are separated by flash chromatography (silica gel, EtOAc/cyclohexane 1 9). 

---