Alkenylation aerobic

Under basic conditions, Pd(II) catalyses the bisfunctionalisation of allenyl esters by boronic acids and aldehydes in a one-pot reaction which yields 4,6-disubstituted 5,6-dihydropyran-2-ones 20. The tandem process involves attack by nucleophiles at the 3-position and by electrophiles at C-4 some uncyclised 5-hydroxypent-2-enoic acid derivatives can also be recovered <05JOC6848>. The aerobic cyclisation of O-alkenyl P-ketoamides affords 2,6-dihydropyran-3-ones (Scheme 7) <05OL5717>. 

The protocol was shown to be applicable to the alkenylation of halogenated acetoanilides by Prasad and coworkers [15b]. Amatore et al. [15c] succeeded in decreasing the amount of benzoquinone up to 10mol% by its electrochemical recycling. Liu, Guo, and coworkers [15d] reported aerobic oxidative alkenylation of anilides using Pd(OAc)2/Cu(OAc)2/TsOH. Recently, Lipshutz and Nishikata [15e] conducted the reaction in water in the presence of a surfactant polyoxyethanyl... 

SCHEME 24.32 Representative examples for aerobic alkenylation of arenes. 

Beck EM, Grimster NP, Hatley R, Gaunt MJ (2006) Mild aerobic oxidative palladium(ll) catalyzed C-H bond functionalization regioselective and switchable C-H alkenylation and annulation of pyrroles. J Am Chem Soc 128 2528-2529... 

Copper(I)/TEMPO/NMI-catalyzed Aerobic Oxidation of Alcohols. A novel (bpy)Cu(I)/TEMPO/NMI system has been developed to achieve aerobic oxidation of 1° alcohols and avoid overoxidation. This system gave improved conversion relative to other aerobic oxidation protocols, demonstrating functional group tolerance for a diverse range of substrates bearing aliphatic, aryl, alkenyl, alkynyl, halides, as well as 0-, N-, and 5 -heteroatoms (eq 28). In the presence of unprotected 2° alcohols, 1° alcohols undergo selective oxidation (eq 29). ... 

The Ru(II) catalysed arylation of 0-protected phenols by 2-pyridyl group was already performed under efficient conditions [(Eq. 28)] [101]. Ackermann has now succeeded to perform their oxidative alkenylation with alkyl acrylates and Ru(II)/ AgSbFg catalytic system with Cu(0Ac)2-H20 as oxidant in aerobic atmosphere at orf/to-position of the (7-Py group [(Eq. 74)] [158]. The ortho C-H bond activation of these substrates is providing a 6-membered metallacycle intermediate by contrast to all the previous examples of alkenylation taking place via a 5-membered metallacycle. The phenol can be obtained from the alkenylated O-2-Py product by successive treatment with MeOTf and sodium in methanol without transformation of the alkenyl ester group and with tolerance of p-C, p-COR, p-CO, or P-NO2 arene substituent. 

He J, Yamaguchi K, Mizuno N (2011) Aerobic oxidative transformation of primary azides to nitriles by ruthenium hydroxide catalyst. J Org Chem 76(11) 4606-4610 Zhou W, Xu J, Zhang L, Jiao N (2010) An efficient transformation from benzyl or allyl halides to aryl and alkenyl nitriles. Org Lett 12(12) 2888-2891... 

Huang X, Li X, Jiao N (2015) Copper-catalyzed direct transformation of simple alkynes to alkenyl nitriles via aerobic oxidative nincorporation. Chem Sci 6 6355-6360... 

Chiba and coworkers developed a Cul-catalyzed intramolecular aerobic [3-h2] annulation reaction of Af-alkenyl amidines to bi- and tricyclic amidines under O2 atmosphere (Scheme 8.45). A putative nitrene intermediate which might be generated under CUI/O2 system is proposed for this transformation. And this nitrene intermediate could react with C=C double bond of the substrate as a 1,3-dipole with the activation of C(sp2)—H bonds to give the desired products [83]. 

Scheme 8.45 Cul-catalyzed intramolecular aerobic [3h-2] annulation reaction of N-alkenyl amidines to bi- and tricyclic amidines.

In 2006, Gaunt and co-workers described a regioselective alkenylation of pyrroles under mild aerobic oxidative conditions. A catalytic amount of palladium acetate was able to selectively functionalize tert-butojycarbamate (BOC)-protected pyrrole at the C2-position while a C3-selectivity was achieved with triisopropylsilyl (TIPS)-protected pyrroles (Scheme 9.4). The aerobic conditions worked well for reactive alkenes such as acrylate derivatives, nevertheless the use of peroxide ( BuOOBz) appeared necessary in order to achieve good yields with more challenging substrates [i.e., methyl vinyl sul-fone). Interestingly, intermolecular alkenylation of pyrrole can also be effected with complete selectivity and good yields. 

Intermolecular direct C(3)-alkenylation of indoles using palladium(II) as catalyst and oxygen as the oxidant has been achieved. The reaction shows complete regio- and stereo-selectivity all products are ii-isomers at the C(3)-position, and no Z-isomers or 2-substituted products are detected. Aerobic a, -dehydrogenation of aldehydes and ketones is catalysed by Pd(TFA)2/4,5-diazafluorenone. The cleavage of a-C-H bond of the ketone has been identified as the turnover-limiting step of the catalytic mechanism. ... 

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