Table 1 Optimization of Reaction Conditionsa

From: Expedient access to bora-butenolide bioisosteres by counteranion-mediated trans-hydroboration of alkynes

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Entry

X equiv. base

Borane

Time (h)

Yield (%)b

1

1.1 equiv. nBuLi

HBpin

4

0

2

1.1 equiv. LDA

HBpin

4

8

3

1.1 equiv. tBuOLi

HBpin

4

0

4

1.1 equiv. LiHMDS

HBpin

4

20

5

1.1 equiv. NaH

HBpin

4

< 5

6

1.1 equiv. NaNH2

HBpin

4

0

7

1.1 equiv. NaHMDS

HBpin

4

28

8

1.1 equiv. KHMDS

HBpin

4

25

9

1.5 equiv. NaHMDS

HBpin

4

65

10

2.0 equiv. NaHMDS

HBpin

4

70 (64)c

11

2.0 equiv. NaHMDS

HBpin

6

86

12

2.0 equiv. NaHMDS

HBpin

12

85

13

2.0 equiv. NaHMDS

BH3

6

73

14

2.0 equiv. NaHMDS

HBCat

6

35

15

2.0 equiv. NaHMDS

9-BBN

6

0

16

2.0 equiv. NaHMDS

BH3•SMe2

6

0

  1. a1 (0.2 mmol), base and borane (0.4 mmol) in THF (2 ml) at room temperature, then quenching with NH4Cl solution. bisolated yield. c1,4-dioxane as a solvent.
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