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. Author manuscript; available in PMC: 2013 Sep 21.
Published in final edited form as: J Org Chem. 2012 Sep 4;77(18):7932–7944. doi: 10.1021/jo301064u

Table 1.

Base Induced Boroxinate Formation from (S)-VAPOL and B(OPh)3.a

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entry base (S)-VAPOL 3 (% unreacted)b % yield 10 (B1)c % yield 11 (B2)d % yield 9 (B3) 9 9 (B3) δ (ppm) (1H; 11B)e
1 Et3N 8 <1 <1 63 9b 10.25, 5.37
2 i-Pr2NH <1 <1 <1 74 9c 10.31, 5.18
3 Ar2CHNH2 f 3 <1 <1 50 9d 10.37, 5.48
4 Ar2CHN=CHPh f,g 11 <1 <1 76 9a 10.31, 5.51
5 C6H5NH2 24 <1 <1 61 9e 10.29, 5.56
6 N2CHCO2Et h 15 <1 <1 <1 9f – – – –
7 MeCONMe2 32 <1 24 18 9g 10.15, 5.78
8 t-BuCHO 37 <1 33 <1 9h – – – –
9 C6H5CHO 52 <1 27 <1 9i – – – –
10 no base 57 5 18 <1 9j – – – –
a

0.20 mmol of base where added to a solution of 0.10 mmol of (S)-VAPOL and 0.30 mmol of commercial B(OPh)3 in 1.0 mL of CDCl3 at 25 °C and allowed to stir 10 min before spectra were taken. All yields are 1H NMR yields with Ph3CH as internal standard.

b

Bay region doublet at δ = 9.77 ppm.

c

Bay region doublet at δ = 9.55 ppm.

d

Bay region doublet at δ = 9.22 ppm.

e

Chemical shifts for bay region doublet in 1H NMR and four-coordinate boron in 11B NMR.

f

Ar = 3,5-Me2-4-OMeC6H2 (imine 1a, Scheme 1); Ar2CH = MEDAM, see Table 2.

g

Reference 6a.

h

This reaction produces an 80% yield of the mono-alkylation product 12 (Scheme 2).