A Route to Carbasugar Analogues - Jonathan Clayden - The ...

3.1 – Oxazoline synthesis
mCPBA
O
NH 4 OH, MeOH
Ph
Ph
Ph
Ph
CH 2 Cl 2
Ph Ph Conditions
90%
179
HO NH 2
± 175
Entry NH 4 OH:MeOH Temp / °C Time 175 (SM) / %
a 1:1 100 Δ 24 hr 55 (25)
b 3:1 120 µω 2 min 15 (85)
c 3:1 140 µω 20 min 93 (5)
Table 3.1 – synthesis of racemic amino alcohol
The improvement seen under microwave conditions is believed to be due to the use of
a sealed vessel increasing the partial pressure of ammonia, but is also assisted by a
particularly easy isolation which only requires filtration of the cool reaction mixture.
The synthesis of ±175 would be made particularly atom efficient if an oxidant such as
dimethyldioxirane or hydrogen peroxide were used for the epoxidation. 128
3.1.4 Oxazoline synthesis
The availability of only two of the three amines in near optical purity meant that the
amide and aziridine methods (Scheme 3.9) are the remaining viable routes to the
synthesis of enantiomerically pure diphenyl oxazolines. It is important to note that the
amine syntheses above allow either enantiomer to be synthesised. The third method is
still presented below, since it allows the synthesis of racemic diphenyl oxazoline as
well as most of the other oxazolines studied in the previous chapter.
102