Enantiomerically Enriched Tris(boronates): Readily Accessible Conjunctive Reagents for Asymmetric Synthesis

Abstract

The catalytic enantioselective diboration of vinyl boronate esters furnishes chiral tris(boronates) in a selective fashion. Subsequent deborylative alkylation occurs in a diastereoselective fashion, both for intermolecular and intermolecular processes.

Cobalt-Catalyzed 1,1-Diboration of Terminal Alkynes: Scope, Mechanism, and Synthetic Applications

“…Accordingly, its use with 1,1-diborylalkenes could proceed via intermediacy of a stabilized α -borylcobalt intermediate. 35 As shown in Scheme 8, sequential 1,1-diboration-hydroboration of terminal alkynes involving ( Cy APDI)CoCH 3 ( 1 ) and (Terpy)Co(CH 2 SiMe 3 ) ( 14 ) 34 furnished a collection of 1,1,1-triboronates 19 in 50–76% yield over two steps. Importantly, carbonyl-based functional groups were compatible with this hydroboration protocol, as evidenced by the synthesis of triboronates 19e , 19i , and 19g .…”

Selective Boryl‐Anion Migration in a Vinyl sp2−sp3 Diborane Induced by Soft Borane Lewis Acids

“…[11][12][13][14][15][16][17] We hypothesised that an alternative route to induce intramolecular 1,2-boryl-anion migration would be the activation of an unsaturated R À group (e.g. [19][20][21][22] Thes elective (for intramolecular 1,2-boryl migration) activation of [(vinyl)B 2 Pin 2 ] À (complex B,Scheme 1, bottom), requires judicious choice of the borane,B R 3 ,a sarange of outcomes are feasible,i ncluding:i )vinyl-anion transfer from B to BR 3 ;i i) binding of BR 3 to an oxygen atom in B and subsequent CÀOorB ÀOcleavage;iii){BPin} À anion transfer from B to BR 3 ;i v) BR 3 activation of the vinyl p system and intramolecular {BPin} À transfer.W hile (i)a nd (ii)a re undesirable,p athway (iii)w ould be an attractive route to unsymmetrical diboranes using commercial Grignard reagents as activators.E qually notable and our primary focus,i ntramolecular 1,2-boryl migration (pathway (iv)) would be anew and simple route to 1,1,2-triborylated alkanes. This approach is attractive as it avoids prefunctionalization of the carbanion activator.I ti sc onceptually related to the Zweifel reaction, [18] but the use of borane Lewis acids and {BPin} À as the migrating group will lead to differentially functionalised 1,1,2-triborylated alkanes in one step.Related 1,1-diborylated alkanes have emerged as highly versatile reagents used in selective CÀCb ond formation by the Suzuki-Miyaura coupling reaction or by deprotonation/ deborylation of the diborylated carbon atom.…”

Preparation and Reactivity of Acyclic Chiral Allylzinc Species by a Zinc‐Brook Rearrangement

“…[2] However,ifone could create stereogenic centers in acyclic systems,not through aclassical S N 2reaction between ac hiral electrophile and an achiral nucleophile (Scheme 1, path A), but rather through the reaction of ac hiral nucleophile (that would be used as an ew chiral building block for stereoselective synthesis) with an achiral electrophile,i tw ould broaden the synthetic possibilities in organic synthesis (Scheme 1, path B). [4,5] More recent developments have shown that few main-group organometallic species,s uch as organomagnesium [6] and organolithium, [7] as well as transition-metal species,s uch as alkylcopper [8] and alkylzinc, [9] present some configurational stability under particular circumstances (Scheme 1, path C). [3] To fulfill the requirements of configurational stability for secondary carbanions (R 1 ¼ 6 R 2 = alkyl, A)m etalloids such as organoboronates were intensively investigated.…”