Direct Incorporation of [¹¹C]CO₂ into Asymmetric [¹¹C]Carbonates

Table 1

Optimisation of [¹¹C]1 synthesis.

Entry^a	Base	Trapping efficiency (%)	Temperature (°C)	Solvent	RCY (%)^b
1	Cs2CO3	95.2	25	DMF	24
2	Cs2SO4	1.5	25	DMF	0
3	CsI	4.3	25	DMF	5
4	CsF	33.5	25	DMF	0
6	K2CO3	10	25	DMF	0
7	CaCO3	0	25	DMF	0
8	Cs2CO3	20	25	CH3CN	0
9	Cs2CO3	65	25	DMSO	0
10	Cs2CO3	>95%	65	DMF	33
11^c	Cs2CO3	>95%	100	DMF	82, 74

^aReaction conditions: isopropanol (22 µmol), Cs₂CO₃ (66 µmol), TBAI (66 µmol), and organohalide (66 µmol) in 500 µL DMF, 10 mins from end of delivery (EOD) (). ^bThe nonisolated radiochemical yield determined by radio-HPLC analysis of the crude product. ^c.