My PhD dissertation - Institut Fresnel

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variously substituted furans in good to excellent yields and led to think that the low yields
previously observed were rather due to the phosphorylating reagent itself or a conjunction
the latter and the lithiated furan.
2-Methylfuran was first used as starting substrate and metalated with butyllithium
in tetrahydrofuran at - 75 °C. The transient lithiated species could be efficiently trapped
with the usual triethyl phosphite to afford the tris(5-methyl-2-furyl)phosphine (8) in 92%
yield.
O
1) LiC 4H9, THF, - 75 °C
2) P(OC 2H 5) 3
P
O
8, 92%
Another phosphine was prepared, starting from a heteroaromatic substrate, to
illustrate the versatility of this method. Benzofuran was chosen as substrate since it was of
comparable bulkiness as 2-naphthalene substituent and also because of the ease of
metalation of this motif. Thus, benzofuran was treated with butyllithium in
tetrahydrofuran at - 75 °C to undergo smooth metalation at 2-position, and subsequently
trapped with triethyl phosphite to give tris(2-benzofuryl)phosphine (9) [63] .
O
1) LiC 4H 9, THF
- 75 °C, 2 h
2) P(OC 2H 5) 3
P
O
9, 92%
Finally, the synthesis of a second furylphosphine was endeavored. The possibility
to link the phosphorus ligand on a polymer for an efficient recycling of the catalyst was
found attractive
[ ] 93 . A convenient way to link the final phosphine was to introduce an
alcohol functional group at position-5 in order to avoid any steric hindrance on the
vicinity of the phosphorus center. The preparation of tris(5-hydroxymethyl-2-
furyl)phosphine (13) was thus decided and first tried by direct metalation of furfurol (5-
hydroxymethylfuran) with two equivalents of organolithium reagents, or metalation of
silyl-protected furfurol. Unfortunately, trapping the transient species formed with
iodomethane resulted, in both cases, in complete decomposition of the furan adduct. Since
the presence of the hydroxymethyl chain was believed to cause the instability of the
metalated furfurol, an indirect route to phosphine (13) was followed. Furfural was
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