Dedicated to the memory of Professor Ferenc Fülöp, friend and colleague
Abstract
A few years ago, the synthesis of chiral phosphoric acids supported on chiral BINOL
frameworks was accomplished by T. Akiyama and M. Terada. Subsequent relevant applications
demonstrated the importance of chiral phosphoric acids as privileged chiral inducers
in asymmetric organocatalysis. In the present report, we discuss the development of
novel chiral phosphorodiamidic acids derived from C
2-symmetric trans-1,2-diaminocyclohexane aliphatic frameworks. The preparation of the new chiral Brønsted
acids, based on the intermediacy of a 1,3,2-diheterophospholan-2-oxide moiety, turned
out to be challenging since several plausible synthetic methodologies proved to be
ineffective. Furthermore, the five-membered heterocyclic moiety turned out to be easily
hydrolyzed when exposed to nucleophilic alcohols or water. Complementary to the successful
multistep synthesis reported here, it was possible to obtain crystals of the key precursor
of the desired phosphorodiamidic acid, which proved suitable for X-ray diffraction
analysis and hence to establish important conformational characteristics of the novel
heterocycle.
Key words
chiral phosphorus derivatives - α-phenylethyl moiety - chiral phosphoric acids - chiral
Brønsted acids - asymmetric organocatalysis.
