PREPARATION OF CHLOROETHYLBORONATE


 

PREPARATION OF CHLOROETHYLBORONATE



via Lithiation Carbon Insertion

 

 

Reagent

Eq

Apparatus

 

 

 

Boronate ester SM (MW: 194.6)

1.0

Multi-neck flask

Et20 (Anhy.)

0.5ml/1mmol SM

Mechanical stirrer

CH2Cl2

1.6-2.0

Cold bath

THF (Anhy.)

20ml/1ml CH2Cl2

Liquid N2

n-BuLi (2.5M in Hexane)

1.05

95% EtOH

ZnCl2(in Et2O)

0.65

Make stock solution



Procedure

 

1.      Cool solution of CH2Cl2/THF to -100 oC [1]

2.      Add dropwise (by syringe) n-BuLi [2]

3.      Stir at cold for 35 min ® pale yellow solu tion

4.      Add dropwise (by syringe) SM/Et2O [3] ® homogeneous solution

5.      Quench  w/ZnCl2 (in Et2O) at cold [4]

6.      Warm to R.T. slowly and stir at R.T. for overnight

7.      Concentrate on Rotovac (temp.:< 30 oC) ® yellow oil

8.      Dilute residue w/ petroleum ether and sat. NH4Cl

9.      Extract aqueous layer w/ petroleum ether (2 times)

10.  Filter combine organic layers thru bed of MgSO4

11.  Concentrate on Rotovac (temp.: <30 oC) ® crude as colorless oil

12.  Distill by fractional vacuum

13.  Collect product @ 70 - 75 oC/ 0.05 mmHg

14.  NMR w/ CDCl3.  Yield 62% as colorless oil



Notes:

 

[1]  Use liquid N2 & 95% EtOH to make a slush.  Cool THF to -10 oC before add CH2Cl2

[2]  Run n-BuLi along the side of the cold flask to pre-cool.  Inside temp: -100 oC during addition.  ¯ white (LiCHCl2)

[3]  Inside temp: -100 oC during addition

[4]  ZnCl2 was fused under high vac until glassy form then make stock solution in dried Et2O.  ¯ white. Inside temp:

    -100 oC during addition

JACS 108, pp 810-819 (1986).  Organometallic 2, pp 1543-1545 (1983).  J Organomet Chem 122, pp 145-149 (1976). 

38318-141