Rhodium-Catalyzed Regiodivergent Hydrothiolation of Allyl Amines and Imines

The regiodivergent Rh-catalyzed hydrothiolation
of allyl amines
and imines is presented. Bidentate phosphine ligands with larger natural
bite angles (βn ≥ 99°), for example,
DPEphos, dpph, or L1, promote a Markovnikov-selective
hydrothiolation in up to 88% yield and >20:1 regioselectivity.
Conversely,
when smaller bite angle ligands (βn ≤ 86°),
for example, dppbz or dppp, are employed, the anti-Markovnikov product
is formed in up to 74% yield and >20:1 regioselectivity. Initial
mechanistic
investigations are performed and are consistent with an oxidative
addition/olefin insertion/reductive elimination mechanism for each
regioisomeric pathway. We hypothesize that the change in regioselectivity
is an effect of diverging coordination spheres to favor either Rh–S
or Rh–H insertion to form the branched or linear isomer, respectively.