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. 2018 May 2;140(17):5805-5813.
doi: 10.1021/jacs.8b02124. Epub 2018 Apr 23.

C(alkenyl)-H Activation via Six-Membered Palladacycles: Catalytic 1,3-Diene Synthesis

Mingyu Liu  1 , Pusu Yang  1 , Malkanthi K Karunananda  1 , Yanyan Wang  2 , Peng Liu  2 , Keary M Engle  1
Affiliations

C(alkenyl)-H Activation via Six-Membered Palladacycles: Catalytic 1,3-Diene Synthesis

Mingyu Liu et al. J Am Chem Soc. .

Abstract

A catalytic method to prepare highly substituted 1,3-dienes from two different alkenes is described using a directed, palladium(II)-mediated C(alkenyl)-H activation strategy. The transformation exhibits broad scope across three synthetically useful substrate classes masked with suitable bidentate auxiliaries (4-pentenoic acids, allylic alcohols, and bishomoallylic amines) and tolerates internal nonconjugated alkenes, which have traditionally been a challenging class of substrates in this type of chemistry. Catalytic turnover is enabled by either MnO2 as the stoichiometric oxidant or co-catalytic Co(OAc)2 and O2 (1 atm). Experimental and computational studies were performed to elucidate the preference for C(alkenyl)-H activation over other potential pathways. As part of this effort, a structurally unique alkenylpalladium(II) dimer was isolated and characterized.

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Conflict of interest statement

Notes

The authors declare no competing financial interests.

Figures

Figure 1
Figure 1. Substrate scope (allylic alcohols bishomoallylic amines)a
a Reaction conditions were as in Table1, entry 1 unless otherwise statated. b 20 mol% Pd(OAc)2
Figure 2
Figure 2
Computed energy profile for the formation of 1,3-diene via the γ-C(alkenyl)–H activation of 4-pentenamide substrate
Figure 3
Figure 3
Computed (A) energy profiles and (B) transition states for 5-, 6-, and 7-membered pathways for C–H metalation
Scheme 1
Scheme 1
Approaches to directed alkene functionalization
Scheme 2
Scheme 2
Aerobic reoxidation system
Scheme 3
Scheme 3
Proposed tandem E/Z/isomerization/C–H activation
Scheme 4
Scheme 4
Synthesis of organopalladium complexes 9 and 10.
Scheme 5
Scheme 5
Proposed catalytic cycle
See this image and copyright information in PMC

References

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