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Ji et al. Chem Synth 2022;2:17 https://dx.doi.org/10.20517/cs.2022.27 Page 5 of 11

a a
Scheme 3. Scope of arylboronic acids and aryldiazonium salts . Unless otherwise noted, the reaction was conducted with 2a
(0.2 mmol), 3 (0.2 mmol), 4 (0.1 mmol), Rb CO (0.3 mmol), (R)-1a (0.012 mmol) and Pd dba (0.004 mmol) in MTBE (2 mL) at 0 ºC
2 3 2 3
b
for 48 h under Ar. Isolated yields are shown. The er values were determined by SFC. Et O was used instead of MTBE as the solvent.
2
c d
Guanidine carbonate was used instead of Rb CO . Guanidine carbonate (1.0 equiv) and Rb CO (1.0 equiv) were used instead.
2 3 2 3
solvent, product 5q was produced in 53% yield with a lower er value. In further trials, para-tolylboronic acid
and naphthalen-2-ylboronic acid were employed as coupling partners, and the corresponding products 5r
and 5s were generated in moderate yields with good enantioselectivities. As expected, when the phenyl
diazonium salt and 4-methylboronic acid were used as coupling partners, product ent-5r was obtained in
40% yield with 11:89 er. These results indicate that the range of aryldiazonium salts applicable to this
process is relatively limited.

To further extend the scope of this reaction, we subsequently explored various allyl sulfone substrates
[Scheme 4]. The steric effects of phenyl ring substituents were initially examined. A methyl group at the 4-
position of the phenyl moiety was found not to affect the yield or enantioselectivity, while a tertiary butyl
group decreased the yield (5t-5u). The electronic effect of substituents was also evaluated. Both an electron-
rich methoxy substituent and electron-poor substituents such as fluorine, ester and trifluoromethyl groups
slightly decreased the yield and enantioselectivity (5v-5y). Substrates bearing meta-methoxy-phenyl, 3,5-
dichlorophenyl and 1-naphthyl moieties were also examined. In each case, the corresponding product was
obtained with moderate efficiency and a high level of enantioselectivity (5z-5ab). However, a substrate with