Reduction and coupling reaction of carbonyl compounds by KI/Fe(OH)₃ in aqueous media

Figures & data

Scheme 1. Pinacol coupling reactions for Fe(OH)₃/KI activate carbonyl compounds in aqueous media.

Table 1. Pinacol coupling reaction of benzaldehyde (1.0 mmol) with KI (3.0 mmol) under various conditions.

Entry	Reaction media/mmol	Reaction Temp/°C^d	Pinacol 2^a,b Yields/%	Meso/dl^c
1	KI/H2O (5 ml)	r.t.	/	/
2	KI/H2O (5 ml)	40	/	/
3	KI/H2O (5 ml)/FeCl3 (0.1 mmol)	r.t.	9	1/1.2
4	KI/H2O (5 ml)/Fe2(SO4)3 (0.1 mmol)	r.t.	5	1/1.1
5	KI/H2O (5 ml)/Fe(NO3)3 (0.1 mmol)	r.t.	7	1/1.1
6	KI/HCl (10%, 5 ml)/FeCl3 (0.1 mmol)	r.t.	3	1/2.2
7	KI/H2O (5 ml)/Fe(OH)3 (0.1 mmol)	r.t.	52	1/1.1
8	KI/NaOH (5%, 5 ml)/Fe(OH)3 (0.1 mmol)	r.t.	67	1/1.3
9	KI/NaOH (5%, 5 ml)/Fe(OH)3 (0.2 mmol)	r.t.	65	1/2.1
10^e	KI/NaOH (5%, 5 ml)/Fe(OH)3 (0.1 mmol)/ N2	r.t.	79	1/3.1
11	KI/NaOH (5%, 5 ml)/Fe(OH)3 (0.1 mmol)/N2	40	86	1/5.1
12	KI/NaOH (5%, 5 ml)/Fe(OH)3 (0.1 mmol)/N2	50	81	1/2.1

^aThe isolated products were reported.

^bThe pure products were identified by IR, ¹H NMR, ¹³C NMR and HRMS.

^cThe ratio of meso to dl isomer was determined by the ¹H NMR analysis of crude product mixture.

^dThe reaction time was 12 hr.

^eUnder the protection of nitrogen.

Table 2. KI/Fe(OH)₃ promoted pinacol coupling of carbonyl compounds in sodium hydroxide at 40°C under N₂.

Entry	Substrate 1	Time (h)	2 (Yield/%)^a,b	Meso/dl^c	3 (Yield/%)^a,b
1		12	2a (86)	1.3/1	3a (9)
2		12	2b (83)	1.1/1	3b (6)
3		12	2c (81)	1/1.2	3c (3)
4		12	2d (75)	dl-type	3d (13)
5		12	2e (91)	1.4/1	3e (7)
6		12	2f (87)	13/1	3f (4)
7		12	2g (93)	1.5/1	3g (2)
8		12	2h (73)	dl-type	3h (11)
9		12	2i (52)	1/1.1	3i (17)
10		12	2j (61)	1/1.2	–
11		12	–	–	–
12	CH2O	12	2k (47)	1/1	3j (12)
13	CH3CHO	12	2l (32)	1/1	3k (8)
14		12	–	–	–
15		12	–	–	–
16		12	–	–	–

^aThe isolated products were reported.

^bThe pure products were identified by IR, ¹H NMR, ¹³C NMR and HRMS.

^cThe ratio of meso to dl isomer was determined by the ¹H NMR analysis of crude product mixture.

Scheme 2. The mechanism of reaction for Fe(OH)₃/KI activate carbonyl compounds to form pinacol coupling.