Chemistry Reference
In-Depth Information
acid and the mixture was extracted with dichloromethane. The organic layer was
washed with 5% aq. sodium hydroxide at pH 8, dried over anhydrous sodium sul-
fate, filtered, and concentrated in vacuo to give a viscous brown oil in each case.
Column chromatography (CH
2
Cl
2
) gave oxazoles 1135 as the first-eluting compo-
nents. The oxazoloquinazolines 1134 were eluted subsequently; yields 31-50%.
It has been reported that reaction of trans-1,2-diaminocyclohexane 1136a with
either phosgene or phosgene equivalents such as 1,1
-carbonyldiimidazole, urea, di-
methyl carbonate,ormethyl chloroformate does not give the desired imidazolidin-
2-one 1139a, but rather an oligomeric product [806]. This indicates that the in-
termolecular reaction competes effectively with the intramolecular cyclization, a
result that has some precedent in the reaction of 1,2-diaminoethane (ethylenedi-
amine) with urea [807].
A particularly attractive alternative approach is the introduction of a thiocarbonyl
group, to give the imidazolidine-2-thione 1137, followed by acylation to give 1138,
and finally dethionation to the 1,3-diacylimidazolidin-2-one 1139 [806]. The overall
yield is 70-80%, depending on the particular substituents.
O
COR'
H
H
H
N
R
NH
2
R
R
R'COCl
/Py
N
1. CS
2
2. H
3
O
+
S
S
H
DMAP/CH
2
Cl
2
N
R
R
R
2
H
H
H
COR'
1136a
R = -(CH
2
)
4
-
1136b
R = Ph
1138a
R = -(CH
2
)
4
-
1138b
R = Ph
1137a
R = -(CH
2
)
4
-, yield 94 %
1137b
R = Ph, yield 90 %
COR'
H
R
N
Hg(OAc)
2
CH
2
Cl
2
O
N
R
H
COR'
1139a
R = -(CH
2
)
4
-
1139b
R = Ph
A shorter route, in which carbon disulfide is replaced by carbonyl sulfide, has also
been proposed [806].
COEt
H
H
H
N
NH
2
N
1. NaH
1.
OCS
2. H
3
O
+
O
O
2. EtCOCl
H
N
NH
2
H
H
H
COEt
70 %
91 %
1140
1141
1142
Bis(4-nitrophenyl)carbonate 717 (for a preparation, see Section 4.3.3.2) may be
recommended as a convenient reagent for the introduction of a carbonyl bridge
