Rhodium(I)‐Catalyzed Arylation/Dehydroxylation of tert‐Propargylic Alcohols Leading to Tetrasubstituted Allenes

Abstract

Diverse tetrasubstituted allenes are obtained selectively by the reaction of tert-propargylic alcohols and arylboroxines under rhodium catalysis. The reaction is assumed to proceed through an arylation/dehydroxylation process, which involves b-hydroxide elimination of a b-hydroxy alkenylrhodium intermediate that is generated by regioselective arylrhodation of the tert-propargylic alcohol. In addition, when enantioenriched propargylic alcohol was used to prepare optically active allene, high efficiency of central-to-axial chirality transfer was observed. The application of current method to structural modification of pharmaceutical drugs was also showcased by a highly diastereoselective transformation of mifepristone.

Rh‐Catalyzed Reaction of Propargylic Alcohols with Aryl Boronic Acids–Switch from β‐OH Elimination to Protodemetalation

“…5). To further unveil the factor determining protodematalation over the β‐OH elimination, we conducted the reaction of propargylic alcohol 1a with boronic acid 2a under the previously described β‐OH elimination conditions and 11% NMR yield of allene 10aa was still obtained, however, the protodematalation E ‐ 3aa was formed in 51% yield (Scheme c, eq. 6), indicating the importance of the nature of the boron reagent on the chemoselectivity.…”

“…On the other hand, it has been reported the C—H activation based Rh(III)‐catalyzed reaction of arenes with propargylic alcohols afforded allene products (Scheme a) . Later on, Rh(I)‐catalyzed reaction of propargylic alcohols with (ArBO) 3 affording allenes has also been developed (Scheme b) . In these two protocols the arylmetalation affords Int‐A , which subsequently undergoes β‐OH elimination to form an allene (Scheme c, left).…”

Palladium‐Catalyzed Coupling of Propargylic Alcohols with Boronic Acids under Ambient Conditions

“…Coupling of propargylic alcohols has less been reported due to the difficulty encountered in the step of oxidative addition with a transition metal catalyst . Dou and co‐workers reported Rh‐catalyzed cross‐coupling of propargylic alcohols with arylboroxines affording allenes via S N 2’‐type mechanism (Scheme b) [7a] .…”

“…Coupling of propargylic alcohols has less been reported due to the difficulty encountered in the step of oxidative addition with a transition metal catalyst . Dou and co‐workers reported Rh‐catalyzed cross‐coupling of propargylic alcohols with arylboroxines affording allenes via S N 2’‐type mechanism (Scheme b) [7a] . Yoshida and Ihara found the Pd‐catalyzed direct coupling of propargylic alcohols with arylboronic acids affording allenes and/or alkynes could be achieved at 100 o C (Scheme c, up) [6j] .…”

A Highly Efficient Dimeric Manganese‐Catalyzed Selective Hydroarylation of Internal Alkynes

“…The major challenge for the development of such a transformation involves: a) Suppressing the competing b-oxygen elimination side reactions. [5] b) Regioselectivity independent of the electronic effect of alkynes. [6] c) The interference between multiple reactive functional groups in propargyl alcohols.…”