The bromo unsaturated carbohydrates 3a and 9
were prepared from ethyl 4,6-di-O-acetyl-2,3-dideoxy-d-erythro-hex-2-enopyranoside
(1a) and (7) by deacetylation followed by
monosilylation with
TBDMSCl and then alkylation with
BrCH2CBrCH2. The threo
analogues 6 and 10 were obtained
using the same methodology after inversion at C-4 via a
Mitsunobu reaction. The N- and
C-analogues 4b and 5 were prepared by
palladium alkylation of the carbonate 2d with
TsNHCH2CBrCH2 and
(CO2Me)2CHCH2CBrCH2,
respectively. Treatment of the unsaturated carbohydrates 3a and 9 with a catalytic amount of
Pd(OAc)2/PPh3 in
CH3CN/H2O in the presence of
Bu4NHSO4 and NEt3 afforded the
bicyclic compound 14a. The N- and
C-analogues 14b and 14c
were obtained using the same conditions and starting, respectively,
from 4b and 5. On the other
hand, treatment of the threo derivatives 6 and
10 under these conditions gave the furanic
structure
15. In the case of compound 3a, performing
the reaction in the presence of sodium formate yielded
the bicyclic 2-deoxy carbohydrate 17.
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