Table 1 Optimization of the Reaction Conditions^a


entry	alteration to conditions	yield (%)^b	ee (%)^c
1	none	83	90
2	Eosin Y instead of DPZ	N.R.^d	N.A.
3	Rose Bengal instead of DPZ	N.R.^d	N.A.
4	4CzIPN instead of DPZ	82	89
5	Ir(ppy)₃ instead of DPZ	45	90
6	Ir^III complex^e instead of DPZ	87	89
7	C2 instead of C1	57	75
8	C3 instead of C1	31	58
9	no C1	12	N.A.
10	no DPZ	N.R.	N.A.
11	no light	N.R.	N.A.
12	under air	N.P.	N.A.

^aReaction conditions: 1a (0.10 mmol), 2a (0.12 mmol), DPZ (5.0 × 10^‒4 mmol) and C1 (0.01 mmol) in degassed DCM (5.0 mL) and at ‒35 °C. ^bYield of isolated product. ^cEes were determined by HPLC analysis. ^dAfter 96 h, trace product 3a was observed. ^eIr^III complex = (Ir[dF(CF₃)ppy]₂(dtbbpy))PF₆. N.R. = no reaction. N.A. = not applicable. N.P. = no product. 4CzIPN = 2,4,5,6-tetrakis(carbazol-9-yl)−1,3-dicyanobenzene. ppy = 2-(2-pyridyl)phenyl. dF(CF₃)ppy = 2-(2,4-difluorophenyl)−5-trifluoromethylpyridine. dtbbpy = 4,4-di-tert-butyl-2,2’-bipyridine.

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