Handbook of Functionalized Organometallics Applications in S

R
124
BF 3K
Br
3.3 Preparation and Reactions of Functionalized Alkenyl Boranes
CN
PdCl 2(dppf)·CH 2Cl 2
(2 mol %)
i-PrOH, H 2O, t-BuNH 2
Scheme 3.64 Preparation and cross-couplingreactions of
functionalized alkenyl trifluoroborates.
R
CN
125a: R = Cl-(CH 2) 3: 52 %
125b: R = MeO 2C(CH 2) 3: 33 %
3.3.5
Palladium-catalyzed Cross-coupling of Functionalized Alkenyl Boronates with
Cyclopropyl Iodides
Charette has reported the first cross-coupling reaction of aryl/alkenyl boronic
esters with cyclopropyl iodides [99]. The alkenyl boronates with the protected hydroxy
group gave coupled products in moderate to good yields. Similarly the Pdcatalyzed
cross-coupling of benzyloxymethylcyclopropyl boronate with trans-benzyloxy-methyliodocyclopropane
gave the symmetrical benzyloxy substituted biscyclopropane
in 71% yield (Scheme 3.65) [100].
RO B O
R=Bn
R=TBDMS
BnO B
O
O
O I OBn
Pd(OAc) 2 (0.1 equiv.)
PPh 3
K 2CO 3,Bu 4NCl
I OBn
Pd(OAc) 2 (0.1 equiv.)
PPh 3 (0.5 equiv.)
K 2CO 3,Bu 4NCl
RO
BnO
Scheme 3.65 Cross-couplingof boronic esters with cyclopropyl iodides.
OBn
R=Bn:64%
R=TBDMS:35%
71 %
OBn
3.3.6
Intermolecular Suzuki Cross-coupling Reactions of Functionalized Alkenylborane
Derivates: Application in Natural Product Synthesis (Alkenyl B-Alkenyl Coupling)
Roush has demonstrated that thallium(I) ethoxide promotes Suzuki-coupling for
a range of functionalized alkenyl boronic acids and functionalized aryl or alkenyl
halides in good to excellent yields [101]. This reagent offers distinct advantage over
thallium(I) hydroxide in terms of its commercial availability, stability and ease of
use (Scheme 3.66).
83