Table 1.

Optimizing relative and absolute stereocontrol in transfer hydrogenative carbonyl crotylation from the alcohol oxidation level.^a

Entry	Ligand	Acid	OAc (eq)	THF (M)	T °C	Y (%)	dr (ee%)
1	BIPHEP	A	10	0.2	100	85	2.0:1
2	BIPHEP	B	10	0.2	100	72	2.7:1
3	BIPHEP	C	10	0.2	100	10	2.0:1
4	BIPHEP	D	10	0.2	100	68	2.2:1
5	BIPHEP	E	10	0.2	100	50	1.5:1
6	BIPHEP	F	10	0.2	100	78	2.3:1
7	BIPHEP	G	10	0.2	100	93	2.6:1
8	BIPHEP	H	10	0.2	100	80	2.4:1
9	BIPHEP	I	10	0.2	100	70	3.0:1
10	BIPHEP	J	10	0.2	100	65	3.5:1
11	BIPHEP	K	10	0.2	100	86	2.4:1
12	BIPHEP	L	10	0.2	100	38	1.9:1
13	BIPHEP	M	10	0.2	100	7	1.9:1
14	BIPHEP	N	10	0.2	100	5	2.1:1
15	BIPHEP	I	5	0.2	100	57	3.7:1
16	BIPHEP	I	2	0.2	100	55	4.3:1
17	BIPHEP	I	2	0.5	100	77	4.8:1
18	BIPHEP	I	2	1.0	100	75	7.1:1
19	BIPHEP	I	2	1.0	90	78	7.5:1
20	BIPHEP	J	2	1.0	90	42	7.6:1
21	(S)-BINAP	I	2	1.0	90	75	3.5:1 (95)
22	(S)-MeO-BIPHEP	I	2	1.0	90	63	5.8:1 (94)
23	S)-Cl,MeO-BIPHEP	I	2	1.0	90	67	3.0:1 (96)
⇨ 24	(S)-SEGPHOS	I	2	1.0	90	70	7.4:1 (95)
25	(S)-C2-TUNEPHOS	I	2	1.0	90	68	7.7:1 (91)
⇨ 26	(S)-C3-TUNEPHOS	I	2	1.0	90	77	8.0:1 (97)
27	(S)-C4-TUNEPHOS	I	2	1.0	90	71	6.4:1 (92)

^aAll reactions were performed in 13 × 100 mm pressure tubes. The cited yields are of material isolated by silica gel chromatography. Enantiomeric excess was determined by chiral stationary phase HPLC analysis via comparison to racemic diastereomeric mixtures. For entries 1–18, the reaction was allowed to run for 20 hours. For entries 19–27, the reaction was allowed to run for 48 hours. See experimental section for further details.