Palladium‐Catalyzed Oxidative Cyclization of Enynes with Hydrogen Peroxide as the Oxidant

Abstract

Gently does it: The Pd‐catalyzed oxidative cyclization of enynes with hydrogen peroxide, a simple, inexpensive, and environmental benign oxidant, is proposed to proceed through a catalytic PdII/PdIV cycle in which the key CCl bond‐forming step is the formation of a PdIV intermediate (see scheme). This is followed by a direct reductive elimination to generate CCl bonds with retention of the configuration of the C(sp3) center.

The Renaissance of α‐Methylene‐γ‐butyrolactones: New Synthetic Approaches

“…[116] In 2008, Liu and Yin reported the Pd-catalyzed oxidative cyclization of similar enyne substrates (Scheme 42). [117] bChloro-a-methylene-g-butyrolactones 189 were obtained in good to excellent yields predominantly as the Z stereoisomers. It is noteworthy that when 188 was substituted at the allylic position (e.g.…”

“…[ 85] Reaction of the readily prepared [a-(ethoxycarbonyl)alkenyl]diisobutylaluminium 116 with styrene oxide (117) in the presence of BF 3 ·Et 2 O provided …”

“…[84] Subsequently, Ramachandran and co-workers extended their methodology to the synthesis of (Z)-a-alkylidene-g-arylg-butyrolactones 119 by alkenylalumination of the corresponding 2-aryloxirane 117. [85] Reaction of the readily prepared [a-(ethoxycarbonyl)alkenyl]diisobutylaluminium 116 with styrene oxide (117) in the presence of BF 3…”

High‐Oxidation‐State Palladium Catalysis: New Reactivity for Organic Synthesis

“…In this case, the opposite relative configuration of the products pointed to a direct reductive elimination from within the coordination sphere of the Pd IV catalyst. [78] 6. Mechanistic Basis for Reductive Elimination from s-Alkyl Palladium(IV) Catalysts…”

Palladium‐Catalyzed Oxidative Carbocyclizations

“…Liu and co-workers reported a palladium-catalyzed dichlorination of enynes, similar to that by Lu (Schemes 60 and 63), [65,68] using a simple and environmentally benign oxidant, hydrogen peroxide (Scheme 94). [90] The authors proposed that this reaction proceeds through a Pd II /Pd IV cycle in which the secondary C sp 3 À Cl bond is formed with retention of configuration at the C sp 3 center, through a direct reductive elimination according to the stereochemical study on the transformation of (E)-59 and (Z)-59 (Scheme 95). This result is consistent with Lus discovery in the Pd II /Pd 0 cycle.…”