Transition metal-free ether coupling and hydroamidation enabling the efficient synthesis of congested heterocycles.

In this study, we discovered that α-bromocarboxamides react with alkynols containing tertiary alcohol moieties to produce congested ethers or heterocycles. Here, the etherification and hydroamidation reactions can be controlled by a suitable base. Both C-O and C-N bond formations occurred without a transition-metal catalyst. The stereospecific etherification and cyclization of diastereo-enriched α-bromocarboxamide afforded the corresponding diastereo-enriched ether and heterocyclic compound.

Chemistry of Tertiary Carbon Center in the Formation of Congested C-O Ether Bonds.

Nucleophilic substitutions, including SN 1 and SN 2, are classical and reliable reactions, but a serious drawback is their intolerance for both bulky nucleophiles and chiral tertiary alkyl electrophiles for the synthesis of a chiral quaternary carbon center. An SRN 1 reaction via a radical species is another conventional method used to carry out substitution reactions of bulky nucleophiles and alkyl halides, but chiral tertiary alkyl electrophiles cannot be used. Therefore, a stereospecific nucleophilic substitution reaction using chiral tertiary alkyl electrophiles and bulky nucleophiles has not yet been well studied. In this paper, we describe the reaction of tertiary alkyl alcohols and non-chiral or chiral α-bromocarboxamides as a tertiary alkyl source for the formation of congested ether compounds possessing two different tertiary alkyl groups on the oxygen atom with stereoretention.