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

Table 2

Optimisation of [¹¹C]1 synthesis using alternative bases.

Entry^a	Base (eq)	TBAI (eq)	Temp (°C)	RCY (%)^b
1^c	DBU (3)	3	100	6
2^c	DBU (3)	—	100	0
3	NaH (1)	1	100	26
4^d	NaH (1)	1	60	31 ± 2
5^c	NaH (0.5)	1	60	18
6	NaH (2)	1	60	0
7^c	NaH (0.5)	—	60	6
8	NaH (1)	3	60	7

^aIsopropanol (1 equiv., 22 µmol), BzCl (3 equiv.), TBAI (1–3 equiv.), and base (1–3 equiv.) in 500 μL DMF reaction time 5 mins from EOD. ^bThe nonisolated radiochemical yield determined by radio-HPLC analysis of the crude product. ^cReaction time of 10 mins from EOD.^d.