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(%) 367 (60), 308 (72), 262 (8), 105 (100); EI-HRMS calcd for C22H25N1O4 m/z [M] + 367.1784;
found 367.1771.
[Rh(dppb)(CO)2]BF4 (325). [Rh(cod)2]BF4 (30 mg, 0.074 mmol) was placed in an oven-dried
25 mL Schlenk flask under Ar, and DCE (3 mL) was added to form a dark red solution. Then a
solution of dppb (34 mg, 0.081 mmol) in DCE (2 mL) was added via a syringe over 1 min and
the reaction mixture turned bright yellow. The atmosphere was replaced with CO via a balloon
and the reaction vessel was immersed in an oil-bath preheated to 70 °C and stirred for 5 min.
After cooling to rt, the solution was transferred to an oven-dried test tube under Ar via a canula
and Et2O (10 mL) and hexanes (2 mL) were added to form a yellow precipitate. The test tube
was centrifuged for 15 min, and the pale yellow liquid was removed via a syringe. After removal
of the residual solvent under vacuum, 325 (45 mg, 91%) was obtained as a yellow powder.
Note: this complex was stored under Ar at -10 °C and used for up to two weeks without
noticeable effect on the performance in the cyclocarbonylation reaction.
31 P NMR (121.4 MHz, CDCl3, external standard H3PO4): δ 21.40 (d, J = 119.7 Hz); IR (thin
film): ν 2024 (CO), 1481, 1435, 1049 cm -1
BzN O
MeO 2C
H
2-Benzoyl-1,4-dimethyl-6-methylene-5-oxo-1,2,3,5,6,6a-hexahydrocyclopenta[c]pyrrole-1-
carboxylic acid methyl ester (288c). To a solution of allenyne 74c (21 mg, 0.071 mmol) in
DCE (1.4 mmol) in a new 15 mL test tube was added [Rh(CO)2(dppb)]BF4 (2 mg, 3 µmol) under
Ar atmosphere. The test tube was sealed with a rubber septum and CO (3 mL) was injected via a
syringe. The reaction vessel was heated to 80 °C for 1.5 h, and then cooled to rt and filtered on a
plug of silica gel eluting with EtOAc : hexanes 1 : 1 to afford a mixture of products (26 mg,
288c
278