Table 1. Optimization of the Hydroboration Reaction^a.

entry	4	solvent	H source	yield (%)b	rrc	erd
1e	4c	THF	i-PrOH	0	N/A	N/A
2	4a	THF	i-PrOH	1	77:23	N/A
3	4b	THF	i-PrOH	7	97:3	90:10
4	4b	THF	MeOH	23	95:5	89:11
5	4b	THF	TFE	1	94:6	N/A
6	4b	THF	t-BuOH	2	95:5	N/A
7	4b	THF	H2O	15	95:5	89:11
8	4b	THF	BzOH	1	98:2	N/A
9	4b	DME	H2O	33	97:3	89:11
10	4b	heptane	H2O	48 (44)	98:2	89:11
11f	4b	heptane	H2O	79 (76)	98:2	90:10
12f	4a	heptane	H2O	3	80:20	N/A
13f,g	4c	heptane	H2O	(38)	95:5	90:10
14f	4d	heptane	none	63	25:75	77:23

^aReactions conducted with 0.38 mmol 2a.

^bYields determined by GC analysis by using biphenyl as an internal standard; yields of isolated product in parentheses.

^cThe branched/linear ratio (rr) was determined by GC analysis of the crude reaction mixture.

^dDetermined by chiral SFC analysis following oxidation of 3a.

^e5 mol % NaOt-Bu was used as an additive; reaction conducted at 60 °C; diboration product 5 was isolated in 86% yield, 98:2 er.

^fReaction conditions: 5 mol % catalyst 1a, 1.5 equiv boron source 4, 6 equiv proton source, 1 M concentration, 40 °C, 16 h.

^gDiboration product 5 was isolated in 6% yield, 81:19 er.