Chemistry Reference
In-Depth Information
H
2
NC(CH
2
CH
2
CO
2
CMe
3
)
3
[33,36,37]. Although the original procedure used Raney
nickel in EtOH [32], when n-heptane was used for the hydrogenation, the amine was
isolated in 98% yield with an increased melting point [38].
Di-tert-butyl 4-[2-(tert-butoxycarbonyl)ethyl]-4-isocyanatoheptanedioate, OCNC-
(CH
2
CH
2
CO
2
CMe
3
)
3
, was formed by treatment of H
2
NC(CH
2
CH
2
CO
2
CMe
3
)
3
with phosgene or triphosgene [39-43]. The related, divergently generated G2
and G3 dendrons were similarly formed [44]. A convergent procedure [45], which
utilized O
2
NC(CH
2
CH
2
CO
2
H)
3
, derived from hydrolysis (HCO
2
H) of O
2
NC-
(CH
2
CH
2
CO
2
CMe
3
)
3
,followedbyH
2
NC(CH
2
CH
2
CO
2
CMe
3
)
3
using standard ami-
dation (HOBTand DCC) and then reduction using Raney-nickel generated the related
G2 and G3 dendrons. A series of these isocyanates [17,39,42,43] and their use in
combinatorial chemistry [40,46] has been reported in which O
2
NC[(CH
2
)
3
CN]
3
[47]
was reduced (BH
3
-THF) to O
2
NC[(CH
2
)
3
NH
2
]
3
, which was Boc-protected giving
O
2
NC[(CH
2
)
3
NHBoc]
3
,
then reduction [Ni(R), H
2
]
to the
amine H
2
NC-
[(CH
2
)
3
NHBoc]
3
and lastly conversion to the isocyanate O
¼
C
¼
NC[(CH
2
)
3
NHBoc]
3
with triphosgene [48] or DMAP and (Boc)
2
O [49]; [R
¼
2,6-Pyridine [50];
