Chirality Transfer in Gold(I)-Catalysed Hydroalkoxylation of 1,3-Disubstituted Allenes

Abstract

Gold(I)-catalysed intermolecular hydroalkoxylation of enantioenriched 1,3-disubstituted allenes was previously reported to occur with poor chirality transfer due to rapid allene racemisation. The first intermolecular hydroalkoxylation of allenes with efficient chirality transfer is reported here, exploiting conditions that suppress allene racemisation. A full substrate scope study reveals that excellent regio- and stereoselectivities are achieved when a σ-withdrawing substituent is present.

Keywords: alcohols; allenes; chirality transfer; ether; gold.

Scheme 1

Previous work on intermolecular gold‐catalysed hydroalkoxylation of allenes.

Scheme 2

1,3‐Disubstituted allenes can in principle undergo chirality transfer.

Scheme 3

Previous reported attempts at chirality transfer in gold‐catalysed hydroalkoxylation of allenes.

Scheme 4

Addition of molecular sieves (MS) affects efficiency of chirality transfer.

Scheme 5

Initial attempts at increasing the levels of chirality transfer.

Scheme 6

Control reaction to test whether the products 6 racemise under the reaction conditions.

Scheme 7

Effect of solvent and temperature on allene racemisation.

Scheme 8

Reaction to ascertain that regioselectivity is due to inductive effects.

Scheme 9

Postulated origin of stereoselectivity.