Palladium‐Catalyzed Chemoselective Allylic Substitution, Suzuki–Miyaura Cross‐Coupling, and Allene Formation of Bifunctional 2‐B(pin)‐Substituted Allylic Acetate Derivatives

Abstract

A formidable challenge at the forefront of organic synthesis is the control of chemoselectivity to enable the selective formation of diverse structural motifs from a readily available substrate class. Presented herein is a detailed study of chemoselectivity with palladium-based phosphine catalysts and readily available 2-B(pin)-substituted allylic acetates, benzoates, and carbonates. Depending on the choice of reagents, catalysts and reaction conditions, 2-B(pin)-substituted allylic acetates and derivatives can be steered into one of three reaction manifolds: allylic substitution, Suzuki-Miyaura cross-coupling, or elimination to form allenes, all with excellent chemoselectivity. The studies on chemoselectivity of Pd catalysts in their reactivity with boron-bearing allylic acetate derivatives led to the development of diverse and practical reactions with potential utility in synthetic organic chemistry.

Allylic Amination of Pd(II)-Allyl Complexes via High-Valent Pd Intermediates

“…Pd II (allyl) complexes have been previously established as intermediates toward forming allylic substitution products such as allylamine and allyl acetate. − The reaction conditions usually require higher temperatures or longer reaction times for the Pd 0/II -catalyzed allylic substitution reactions. , Recent reports reveal three chemical oxidants (PhI­(OAc) 2 , PhICl 2 , and NFTPT) that have been used to oxidize the Pd II complexes to the stable Pd IV complexes containing a OAc, Cl, or F ligand. − These Pd IV complexes can undergo fast reductive elimination to make C–Cl, C–F or C–OAc bond formation products. Since our [( Me N4)­Pd II (η 3 -allyl)] + complexes proved to be easily oxidized to high-valent Pd species, we performed preliminary investigations of the reactivity of 2 + , 3 + , and 4 + toward C–Cl and C–OAc bond formations using PhICl 2 and PhI­(OAc) 2 . , However, we did not observe Pd IV complexes bearing OAc or Cl ligands, nor C–Cl or C–OAc bond formation products from the reaction of 2 + – 4 + with PhICl 2 and PhI­(OAc) 2 (Table S2).…”

Enantiospecific Synthesis of 1,3‐Disubstituted Allenes from Propargylic Carbonates through a Borylation‐1,2‐Elimination Process

“…Alkenyl boronates have received less attention to prepare allenes through 1,2‐eliminations [15,16] . In 2014, Walsh and col [16] .…”

Propargyl Hydrazides as Useful Intermediates Leading to Pyrazoles via Reaction with Certain Electrophiles

“…1‐Phenylhepta‐1,2‐diene (33): To a nitromethane (1.0 mL)/H 2 O (0.20 mL) solution of 2‐(1‐phenylhept‐2‐yn‐1‐yl)‐ p ‐tolylsulfonylhydrazine ( 2 ) (50 mg, 0.14 mmol) was added tetrabutylammonium hydrogensulfate (4.8 mg, 0.014 mmol) and lanthanum triflate (8.2 mg, 0.014 mmol). The reaction mixture was refluxed for 0.5 h and then poured into a satd.…”