PtCl₂-Catalyzed Cycloisomerizations of Allenynes

Abstract

The PtCl2-catalyzed cycloisomerization of allenyne systems has been examined. This process is a highly versatile tool for obtaining products that cannot be attainable with other metals. Simple adjustment of the allene or alkyne substitution can direct the reactivity in a selective manner and give birth to important carbocyclic frameworks (hydrindenes, cyclic vinylallenes, and trienes).

1,1‐Divinylallene

“…[28] The first cycloaddition occurs at either one of the two equivalent vinylallene "diene" sites of 3 to give mono-adduct 12, a cyclic cross-conjugated triene. [29] The second addition must occur at the semicyclic diene site of 12, with the dienophile approaching from the less hindered p-diastereoface of the diene (i.e. anti with respect to the succinimide ring of 12) and through the expected endo-mode.…”

Gold(I)‐ and Gold(III)‐Catalyzed Cycloisomerization of Allenynes: A Remarkable Halide Effect

“…[7] Our initial experiments with PtCl 2 and precursors 1 (Tables 1 and 2) gave three types of reaction evolution depending upon the substitution pattern of the starting material. [8] To rationalize the formation of products 2-4, we proposed the intervention of a common platinacyclopentene intermediate. This suggestion was later supported by the DFT calculations of Soriano and Marco-Contelles.…”

Experimental and Theoretical Investigation of Hydrogenative Cyclization of Allenynes

“…Allenynes with 2-naphthyl, 2-anisol, and 3-anisol groups underwent cyclization and provided the corresponding products in 73, 65, and 72 % yield, respectively (Table 2, entries [4][5][6]. The cyclization of TMSsubstituted compound 7a gave a lower yield (33 %) compared with the aromatic substituted substrates (Table 2, entry 7).…”

“…Accordingly, studies on reductive cyclization of allenynes that aim to assess the product distribution and the related reaction mechanism are of interest. [3][4][5][6] We expect that our experimental results and theoretical calculations on reductive cyclization of allenynes will contribute to a better understanding of the reactivity and selectivity of allenyne cyclization under hydrogenative conditions. Recently, our research group studied platinum-catalyzed, hydrogen-mediated, reductive cyclization by using a wide range of π-functional groups: bis(enones), enone-aldehydes, alkyne-alkenes, alkyne-α,β-unsaturated carbonyl compounds, alkyne-dienes, alkyne-aldehydes, and allene-hydrazones.…”