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in 1M HCl/dioxane (1 : 1) for 1h, the hydrolysis product was not observed and the starting
material was recovered in ~80% yield. The stability of the imino-oxazolidinone in this
compound to acidic conditions is in sharp contrast to the bicyclic-triene 155a which is readily
hydrolyzed in presence of aqueous acid. g Next, an attempt was made to cleave the imino-
oxazolidinone under Lewis acid conditions, by using a combination of BF3OEt2 and Me2S
(conditions that have been utilized previously to cleave a Cbz protecting group). 107
Unfortunately, these conditions did not effect the desired transformation either (starting material
was recovered in 86% yield). On the contrary, treatment of 156a with LiOH in THF/H2O caused
complete decomposition. 108
Since both acidic and basic conditions failed to cleave the imino-oxazolidinone moiety in
156a, its susceptibility to primary amines as nucleophilic reagents was next examined. To this
end, a solution of 156a in CDCl3 was treated with benzylamine and the reaction was followed by
1 H NMR.
Scheme 3.30 Reaction of 156a with benzylamine.
MeO 2C
O
O
O
N
H
N
Bn
O
N
Ph
O
BnNH 2 (10 equiv.)
CDCl 3, rt
MeO 2C
Bn
O
O
NH
O
N
H
NH
Bn
O
N
Ph
O
NHBn
olefin
isomerization
MeO 2C
Bn
O
O
NH
O
N
H
NH
Bn
O
N
Ph
156a 159a 160a
Although cleavage of the oxazolidinone moiety occured as established by the appearance of new
amide and urea N-H resonances in the downfield region (8-9 ppm), a gradual disappearance of
both olefinic peaks of the diene was observed. Based on these observations, it was speculated
g Personal communication by Dr. Bingli Yan
59
O
NHBn