Table 1 Optimization of reaction conditionsa

From: Facile access to bicyclo[2.1.1]hexanes by Lewis acid-catalyzed formal cycloaddition between silyl enol ethers and bicyclo[1.1.0]butanes

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Entry

Lewis acid

Solvent

Resultsb

1

Cu(OTf)2

DCM

3a (5%), 4 (45%)

2

Zn(OTf)2

DCM

3a (14%), 4 (57%)

3

Ni(OTf)2

DCM

3a (3%), 4(45%)

4

AgOTf

DCM

3a (6%), 4 (46%)

5

Sc(OTf)3

DCM

3a(56%)

6

B(C6F5)3

DCM

4 (43%)

7

Eu(OTf)3

DCM

3a (84%)

8

Gd(OTf)3

DCM

3a (74%)

9

Tm(OTf)3

DCM

3a (92%)

10

Lu(OTf)3

DCM

3a (90%)

11

Yb(OTf)3

DCM

3a (97%)(96%)c

12

YbCl3

DCM

n.r.

13

Yb(OAc)3

DCM

n.r.

14

Yb(OTf)3

toluene

3a (98%)(98%)c

15

Yb(OTf)3

THF

3a (42%)

16

Yb(OTf)3

MeCN

3a (63%)

17

-

DCM

n.r.

  1. aReactions were run on a 0.10 mmol scale, with 0.10 mmol silyl enol ethers 1a, 0.13 mmol BCB 2a, and 0.01 mmol Lewis acid.
  2. bYields were determined by 1H NMR analysis of the unpurified reaction mixture with 1,1,2,2-tetrachloroethane or 1,3,5-trimethoxybenzene as an internal standard.
  3. cYield of the reaction with 5 mol% of Yb(OTf)3.
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