Chemistry Reference
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0.83 equiv. KOH
1 equiv. 18-crown-6
MBM
30 s
-1
, 1 h
R
2
O
R
2
R
3
+
R
1
OH
R
3
R
1
R
2
R
3
R
1
R
2
OH
20 mol% InCl
3
·4H
2
O
MBM
30 s
-1
, 1 h
+
R
3
O
OH
R
1
R
1
= (hetero) aryl, alkyl
R
2,3
= (hetero) aryl, (cyclo) alkyl
Scheme 2.34
Synthesis of propargyl alcohols by nucleophilic addition and their
reaction to give naphthopyrans.
Alkynylation of carbonyl compounds is an important means of carbon-
carbon coupling, delivering propargyl alcohols that are of great interest for
synthetic chemistry. Dong et al. developed the solvent-free synthesis of
propargyl alcohols by nucleophilic addition of terminal alkynes to carbonyl
compounds in a ball mill (Scheme 2.34).
61
Reaction occurred in the presence
of KOH and 18-crown-6. Moderate to high yields (54-97%, 18 examples)
could be achieved by milling for 1 h at 30 Hz in a mixer ball mill. On applying
other inorganic or organic bases no product could be obtained. The crown
ether has to be added in stoichiometric amounts otherwise only moderate
yields resulted. In a further reaction step propargyl alcohols were found to
react with 2-naphthol, catalyzed by InCl
3
4H
2
O, to give the corresponding
naphthopyrans (0-97%, 18 examples). In comparison to reactions in solu-
tion higher yields could be achieved in shorter reaction times.
2.10 Summary
Using ball mills as reactor for organic reactions is of considerable interest.
Various carbon-carbon bond forming reactions have been successfully
performed by ball-milling with high eciency. Thereby, ball-milling offers
some advantages over conventional reactions in solutions. Reactions in ball
mills are often characterized by shorter reaction times, higher yields and in
some cases even different products were formed compared to solution based
methods. Furthermore, the avoidance of solvents during ball milling con-
tributes to a greener synthesis by reducing waste and costs.
Abbreviations
Ac
acetyl
Boc
tert-butyloxycarbonyl
Et
ethyl
tBu
tert-butyl
LAG
liquid assisted grinding
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