Synthesis of 1-Azaazulenes from Cycloheptatrienylmethyl Ketone O-Pentafluorobenzoyloximes by Palladium-Catalyzed Cyclization and Oxidation

Abstract

Various 1-azaazulenes are synthesized from cycloheptatrienylmethyl ketone O-pentafluorobenzoyloximes by treatment with a catalytic amount of Pd(dba)2–t-Bu3P (dba = dibenzylideneacetone) and triethylamine in the presence of MS 4A via alkylideneaminopalladium(II) intermediates generated by oxidative addition of the oximes to a Pd(0) complex.

Radical Aza-Cyclization of α-Imino-oxy Acids for Synthesis of Alkene-Containing N-Heterocycles via Dual Cobaloxime and Photoredox Catalysis

“…The Pd-catalyzed cyclization of oxime esters with pendant alkenes was first developed by Narasaka and co-workers, providing a direct method for the synthesis of substituted pyrroles (Scheme a) . Following this seminal work, the access to other heterocyclic/aromatic species with other types of oxime esters was further achieved . Recently, Bower reported the cyclization of γ,δ -unsaturated oxime esters via an oxidative addition or a radical process for the construction of C­(sp 3 )–N bonds, significantly extending the Narasaka–Heck reaction to the formation of stereogenic heterocycles (Scheme a). , …”

Intramolecular aminopalladation of alkenes as a key step to pyrrolidines and related heterocycles

“…Finally, an unprecedented synthetic approach to a variety of 1-azaazulenes was developed by incorporating the c,d-unsaturated moiety in the form of a cycloheptatrienyl group. 27 Good yields for the amino-Heck cyclisation were obtained by using 10 mol% Pd(dba) 2 and 40 mol% P(t-Bu) 3 in the presence of molecular sieves. Successive oxidation of the crude product mixture with MnO 2 yielded the desired product (Scheme 9, eqn ( 18)).…”

Highly Efficient Narasaka–Heck Cyclizations Mediated by P(3,5‐(CF3)2C6H3)3: Facile Access to N‐Heterobicyclic Scaffolds

“…Importantly, the oxime ester substrates are readily accessible and further derivatization of the cyclization products is possible by manipulation of either the imine or alkene functionalities.The Pd-catalyzed cyclization of oxime esters with alkenes was first reported by Narasaka, et al and provides an entry to pyrroles via the catalytic generation and trapping of an imino-Pd II intermediate (Scheme 1 b). [3] Applications of the "Narasaka-Heck" method to other heteroaromatic classes [4] and cascade reactions [5] have been reported and the scope of the oxime activating group has been examined. [6] The catalytic generation and trapping of metalated imines has also been exploited in other contexts.…”

“…[7][8][9] In general, methods that are reliant upon this process produce C(sp 2 )ÀN bonds and are therefore not applicable to the synthesis of chiral N-heterocycles. [3][4][5] Extension to the formation of C(sp 3 ) À N bonds is an attractive possibility but, cascade processes aside, [5a,b] general methods that achieve this have not been reported. Of particular relevance to this study is a single example by Fürstner, et al, who showed that cyclization of oxime ester 1 provided 2 in 54 % yield.…”