Pd-Catalyzed Borylative Cyclization of Allenynes and Enallenes

Abstract

Pd-catalyzed cyclization of 1,5- and 1,6-allenynes and 1,5-enallenes with bis(pinacolato)diboron affords synthetically useful allylboronates and alkylboronates under smooth conditions in a formal hydroborylative carbocyclization reaction. One C-C and one C-B bond are formed in a single operation. The reaction outcome implies that different mechanisms operate for the reactions of allenynes and enallenes, respectively, the actual pathway depending on the relative reactivity of the alkyne or the alkene versus the allene moiety. The cyclized boronates obtained can be functionalized by oxidation or allylation reaction with aldehydes.

Control of Selectivity in Palladium‐Catalyzed Oxidative Carbocyclization/Borylation of Allenynes

“…Furthermore, by combining the borylation with a CC bond‐forming cyclization, complex molecules suitable for various further functionalizations could be obtained in one step 8–11. 13b,d Such borylating carbocyclizations have been successfully developed by the group of Cárdenas 9–11.…”

Control of Selectivity in Palladium‐Catalyzed Oxidative Carbocyclization/Borylation of Allenynes

“…Furthermore, by combining the borylation with a C–C bond-forming cyclization, complex molecules suitable for various further functionalizations could be obtained in one step 8–11, 13b,d. Such borylating carbocyclizations have been successfully developed by the group of Cárdenas 9–11.…”

“…Such borylating carbocyclizations have been successfully developed by the group of Cárdenas 9–11. Starting from unsaturated compounds, such as enynes,9 enediynes,10 enallenes,11 and allenynes,11 homoallylic or allylic boronates were prepared under palladium(0) catalysis. For instance, the non-oxidative borylating carbocyclization of allenynes 1 in the presence of bis(pinacolato)diboron (B 2 pin 2 ) yielded two isomers ( 2 and 3 ), where borylation occurred at the allene (Scheme 1 a).…”

“…For instance, the non-oxidative borylating carbocyclization of allenynes 1 in the presence of bis(pinacolato)diboron (B 2 pin 2 ) yielded two isomers ( 2 and 3 ), where borylation occurred at the allene (Scheme 1 a). 11…”

“…Palladium-catalyzed borylating carbocyclizations of allenynes: a) under non-oxidative conditions;11 b) under oxidative conditions;13b c) under selective oxidative conditions. E=CO 2 Me.…”