Cobalt-Catalyzed Diastereoselective Reductive [3 + 2] Cycloaddition of Allenes and Enones

Abstract

Allenes and enones undergo diastereoselective reductive [3 + 2] cycloaddition to form cyclopentanols in very good yields in the presence of CoI2(dppe), zinc, zinc iodide, and water.

Activated Zinc Dust

“…(H) Soon after publishing the quinoline synthesis, Cheng and coworkers 24 published a cobalt-catalyzed reductive [3+2] cycloaddition of allenes with enones to afford cyclopentanols with good diastereoselectivity. The reaction is likely initiated via the reduction of Co(II) to Co(I) by zinc dust.…”

Cobalt‐Catalyzed Intermolecular [2+2] Cycloaddition between Alkynes and Allenes

“…[9] Ogoshi and co-workers reported cobalt-catalyzed [2+ +2] cycloadditions between 1,3enynes and vinylarenes to give 1-alkenylcyclobutenes. [11] Inspired by these precedents, [12][13][14] the present study began with exploration of the reaction between 4-octyne (1a)a nd cyclohexylallene (2a;T able 1; see Tables S1-S3 in the Supporting Information for more detail). [11] Inspired by these precedents, [12][13][14] the present study began with exploration of the reaction between 4-octyne (1a)a nd cyclohexylallene (2a;T able 1; see Tables S1-S3 in the Supporting Information for more detail).…”

“…[4] With alkyne as the other unsaturated reactant, the [2+ +2] cycloaddition leading to a3 -alkylidenecyclobutene skeleton has been extensively explored in intramolecular settings under either thermal [5] or transition metal catalyzed [6] conditions (Scheme 1a). [11] Inspired by these precedents, [12][13][14] the present study began with exploration of the reaction between 4-octyne (1a)a nd cyclohexylallene (2a;T able 1; see Tables S1-S3 in the Supporting Information for more detail). [7c,d] To our knowledge,s elective intermolecular [2+ +2] cycloaddition between electronically unbiased alkynes and allenes under transition-metal catalysis remains elusive,w hereas different types of allene/ alkyne cycloadditions and dimerizations have been reported using rhodium and nickel catalysts.…”

“…[10] More recently,R ajanbabu and co-workers achieved cobaltcatalyzed 1,3-enyne/ethylene [2+ +2] cycloaddition and (asymmetric) hydrovinylation in at andem fashion. [11] Inspired by these precedents, [12][13][14] the present study began with exploration of the reaction between 4-octyne (1a)a nd cyclohexylallene (2a;T able 1; see Tables S1-S3 in the Supporting Information for more detail). With ac atalytic system comprising CoBr 2 (5 mol %), dppf (5 mol %), and In (20 mol %), a1 :1 mixture of 1a and 2a underwent clean conversion in DCE at 60 8 8C, affording the desired [2+ +2] cycloadduct 3aa as as ingle regio-and stereoisomer in 89 % yield (entry 1).…”

A Straightforward Procedure for the [2+2+2] Cycloaddition of Enediynes

“…[12,13] Diels-Alder, [14] homo-DielsAlder reactions, [15] and Alder-ene reactions, [16] [6 + 2], [17] reductive [3 + 2], [18] and [4 + 2 + 2] cycloadditions, [19] cyclizations of o-iodobenzoates with aldehydes, [20] aryl-sulfur bond formations, [21] Reformatsky reactions, [22] cross-couplings and conjugate additions [23] were also performed under these conditions. Therefore, common catalysts of type CpCoL 2 could be replaced by catalytic systems much easier to handle (and sometimes more efficient [11a] ) to generate benzenes or pyridines by [2 + 2 + 2] approaches.…”