Alkenyls reductive coupling

Reductive coupling of acrylates 521 and imines in the presence of iridium provides azetidin-2-ones bearing aromatic, alkenyl, and alkynyl side chains, with high diastereoselection (Equation 213) <2002OL2537>. The reaction has been proposed to occur through a reductive Mannich addition-cyclization mechanism. 

Mechanism The Pd- or Ni-catalyzed alkenyl-alkenyl and alkenyl-aryl coupling reactions may proceed according to Scheme 5.25, involving the oxidative addition, transmetallation and reductive elimination. 

Erker and co-workers (41, 41a) have studied the photochemistry of several zirconium alkenyl complexes and observed both isomerization of the alkenyl ligand and reductive coupling of the alkenyl ligand with X. 

In the reductive coupling of phenylhexenyldichlorosilane, 75% of the alkenyl groups did not react with radicals, although cyclization was highly favored in the strainless ring. This result means that the lifetime of radicals must be very short and that they can be further reduced to silyl anions prior to intramolecular cyclization. The presence of anionic intermediates is additionally supported by faster reactions in ethereal solvents, first-order kinetics of the monomer, and some model reactions. The formation of silyl... 

Zhang, S Zhang, D., Llebeskind, L. S. Ambient Temperature, Ullmann-llke Reductive Coupling of Aryl, Heteroaryl, and Alkenyl Halides. J. Org. Chem. 1997, 62, 2312-2313. 

Interesting coupling reactions can be carried out with alkenyl- and alkynyl-stannanes. Reductive coupling of acid chlorides with ( )-l,2-bis(tri-n-butylstannyl)-... 

By combining the utility of Cu hydride catalysis with the ability of C=N containing azaarenes to activate adjacent alkenes toward nucleophilic additions, the enantioselective reductive coupling of alkenyl azaarene 154 with ketone 155 has been developed by Lam (Scheme 11.34). This process is tolerant to a wide variety of azaarenes and ketones, and provides aromatic heterocycles 157 bearing tertiary-alcohol-containing side chains with high levels of diastereo- and enantioselection via a six-membered chair-like transition state 156 [53]. 

Scheme 11.34 Enantioselective, Cu-catalyzed reductive coupling of alkenyl azaarene with ketone [53].

Aryl, heteroaryl, and alkenyl halides participate in Ullman-like reductive couplings in the presence of 2.5-3.0 equiv of CuTC at ambient temperature in NMP. Aryl iodides and bromides dimerize as long as there is an orfAo-ligating substituent (eq 3). ... 

Various 6 -octylmellblose-based aldehydes fe.q. 42) and related hemiacetals (e.q. 43) have been made by reductive ozonolysis of corresponding alkenyl glycosides for reductive coupling to amino-acid derivatives. ... 

The palladium-catalyzed [4- -2]-benzannulation of diynes by enynes, such as the [2- -2- -2]-trimerization sequence, is accelerated in the presence of a combination of a Lewis acid/phosphine or by a Bronsted base [11]. This allows the reaction conditions to be modified and to increase the number of substrates used and the reaction yield, especially for the synthesis of problematic penta-substituted benzenes. One of the features of the reaction of [4-1-2]-benzannulation is that it requires the presence of an activating group (AG, alkenyl or alkynyl) in the enynophile (2.216, Scheme 2.74). Development of this trend has led to the discovery of three different series of alkynyl trimerization in the presence of Pd(0) catalyst. A formal [2- -2- -2]-trimerization passes through reductive coupling of two identical (R = R, = H) or different R and R groups... 

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