Copper‐Catalyzed Borylation of α‐Alkoxy Allenes with Bis(pinacolato)diboron: Efficient Synthesis of 2‐Boryl 1,3‐Butadienes

Abstract

Eine solide Grundlage: 2‐Boryl‐1,3‐butadiene mit verschiedenen Substitutionsmustern wurden in guten bis hohen Ausbeuten in einer Kupfer‐katalysierten Borylierung von α‐Alkoxyallenen mit Bis(pinakolato)dibor gebildet (siehe Schema; Bn=Benzyl, pin=Pinakolat, L ist ein N‐heterocyclisches Carben). Die Produkte sind nützliche Zwischenstufen für die Synthese von cyclischen Vinylboranen, α,β‐ungesättigten Ketonen und funktionalisierten mehrfach substituierten Dienen.

Synthesis of Functionalized [3], [4], [5] and [6]Dendralenes through Palladium‐Catalyzed Cross‐Couplings of Substituted Allenoates

“…Noteworthy is the realization of substituted enoates at their b-positions (e.g., 3) without observable isomerization. [10] Given the precedent for copper-catalyzed borylations of allenic carbonates that produce 2-borylated 1,3-butadienes, [11] along with the opportunities offered by micellar catalysis for tandem reaction sequences in the same aqueous medium, [7,12] initial carbon-boron bond formation could be followed by a Pd-catalyzed cross-coupling, in 1-pot, furnishing dendralenic derivatives (Scheme 2, C) [6h] Of note is that homocoupling does not occur under copper catalysis even after extended reaction times (i.e., from 2 to 48 h). This multi-catalytic system applied to the synthesis of functionalized dendralenes shows broad substrate compatibility, as well as functional group tolerance.…”

Synthesis of Functionalized [3], [4], [5] and [6]Dendralenes through Palladium‐Catalyzed Cross‐Couplings of Substituted Allenoates

“…Thus,a crylates,a crylamides,s tyrenes,a nd other alkenes readily participated under similar micellar conditions,p roviding the corre-sponding Heck products in good isolated yields.N oteworthy is the realization of substituted enoates at their b-positions (e.g., 3)w ithout observable isomerization. [10] Given the precedent for copper-catalyzed borylations of allenic carbonates that produce 2-borylated 1,3-butadienes, [11] along with the opportunities offered by micellar catalysis for tandem reaction sequences in the same aqueous medium, [7,12] initial carbon-boron bond formation could be followed by aP d-catalyzed cross-coupling,i n1 -pot, furnishing dendralenic derivatives (Scheme 2, C). [6h] Of note is that homocoupling does not occur under copper catalysis even after extended reaction times (i.e., from 2to48h).…”

Efficient Access to Bicyclo[4.3.0]nonanes: Copper‐Catalyzed Asymmetric Silylative Cyclization of Cyclohexadienone‐Tethered Allenes

“…In addition, Cu-Si addition places the Cu at the less-hindered site of the allene,leading to the formation of bsilylated allylcopper intermediate T2,r ather than T1.S uch selective Cu-Si addition, together with the highly reactive nature of cyclohexadienone,c ould potentially avoid the competitive b-elimination pathway for the heteroatomlinked 1,6-enallenes (X = O, N). [17] Thes ubsequent intra-molecular 1,4-addition of T2 furnishes chiral cis-bicyclic framework bearing three consecutive chiral carbon centers. [18] Nevertheless,t he remote control of reaction diastereo-and enantioselectivity (1,8-asymmetric induction) remains quite challenging during this addition process.…”