Ir-Catalyzed Substitution of Propargylic-type Esters with Enoxysilanes

Abstract

Propargylic-type acetates react readily with enoxysilanes in the presence of 1 mol % of [Ir(cod){P(OPh)3}2]OTf activated preliminarily with molecular H2 to give beta-alkynyl ketones in high to excellent yields. Substitution at the propargyl carbon proceeds exclusively or selectively in most types of propargylic esters. Alternatively, the formation of the allenyl products is predominant in the reaction of esters, which have two phenyl groups on the propargyl carbon.

<b>SYNTHESIS OF ALLENIC NAPHTHALENE DERIVATIVES</b>

“…For phenyl propargyl alcohol 3d [11], phenylacetylene was treated with 1-napthaldehyde and butyllithium at -78 o C for 2 h in 75 % yield. After the reaction of proparglic alcohol 3d with acetyl anhydride, acetate formed 4d [12] as a yield of 77 %. Reduction of acetate 4d with SmI 2 in the presence of 2-propanol and catalytic amount of Pd(0), allene 5d and acetylene 6d were generated in yields of 24 % and 55 %, respectively.…”

Copper(II) Triflate‐Catalyzed Nucleophilic Substitution of Propargylic Acetates with Enoxysilanes. A Straightforward Synthetic Route to Polysubstituted Furans

“…Furthermore, the copper(II)-catalyzed substitution proceeded completely in 5 min. Compared with the existing methodologies [6,7] where several hours were required for complete transformation, our procedure needs much lower reaction times. The results exhibit the superiority of CuA C H T U N G T R E N N U N G (OTf) 2 as the catalyst in this type reaction.…”

“…This result implies that the regioselectivity of this substitution is crucially affected by the steric bulkiness at the electrophilic site. It is noteworthy that the corresponding g-alkynyl ketones were obtained in good yields in the examples involving the substrates 1d and 1e which have alkyl groups on the propargylic carbon, and the elimination product enynes 5d and 5e were not observed in the reaction (Table 1, entries 4 and 5), while in the Ir-catalyzed procedure, [6] enynes 5d and 5e were obtained as the major products at 25 8C. Furthermore, the copper(II)-catalyzed substitution proceeded completely in 5 min.…”

“…[3,4] Some transition metal complexes were employed as efficient catalysts for the propargylic substitution reactions of propargylic alcohols with nucleophiles, [2a,b,5] where most of the nucleophiles were heteroatom-centered such as alcohols, thiols, amides and so on; In contrast, carbon-centered nucleophiles were unfortunately limited to allylsilanes for the construction of sp 3 -sp 3 C À C bonds in the reaction. [2b,5h] Recently, Matsuda and coworkers [6] reported that iridium complex [IrA C H T U N G T R E N N U N G (cod)-{PA C H T U N G T R E N N U N G (OPh) 3 } 2 ]OTf serves as a catalyst for the transformation to g-alkynyl ketones by the coupling of propargylic esters with enoxysilanes. Nishibayashis team [7] also described an efficient coupling of propargylic alcohols with ketones for the formation of g-alkynyl ketones and the straightforward synthesis of substituted furans in the presence of catalytic amounts of a ruthenium catalyst.…”

“…[2] Reactions of this type have been traditionally carried out using the Nicholas reaction but with some drawbacks: more than a stoichiometric amount of [Co 2 (CO) 8 ] is required, and several steps are necessary to obtain the propargylic product from propargylic alcohols via cationic propargylic complexes [Co 2 (CO) 6 …”