Oxirane alkynylation

Terminal alkynes react with propargylic carbonates at room temperature to afford the alka-l, 2-dien-4-yne 14 (allenylalkyne) in good yield with catalysis by Pd(0) and Cul[5], The reaction can be explained by the transmetallation of the (7-allenylpailadium methoxide 4 with copper acetylides to form the allenyKalk-ynyl)palladium 13, which undergoes reductive elimination to form the allenyl alkyne 14. In addition to propargylic carbonates, propargylic chlorides and acetates (in the presence of ZnCb) also react with terminal alkynes to afford allenylalkynes[6], Allenylalkynes are prepared by the reaction of the alkynyl-oxiranes 15 with zinc acetylides[7]. 

The 2-(l-alkynyl)oxirane 78 reacts with an organozinc reagent yielding the /9-allenylic alcohol 79[35]. 

Alkynyl)oxiranes also react with carbon nucleophiles to afford furan derivatives. Furanes of different types are obtained depending on the structure of the substrates. 7-Methyl-2-ethynyloxirane (95) reacts with acetoacetate to give the furan 97 by the elimination of formaldehyde from the cyclized product 96. The hydroxy ester of the alkylidenefuran 98 and the corresponding lactone 99 are obtained by the reaction of i-methyl-2-(2-propynyI)oxirane[40, 42]. 

The use of 2-(l-alkynyl)oxiranes 16 [39] or cyclic alkynyl carbonates 17 [40] for the palladium-catalyzed reaction afforded allenylmethyl alcohols 18 and 19, as shown in the representative examples in Scheme 3.10. 

Scheme 6.20. This ruthenium catalyst (10 mol%) was active for the cydization of ds-1 -ethynyl-2-vinyloxiranes to afford various 2,6-disubstituted phenols in reasonable yields. Under similar conditions, 1,1,2,2,-tetrasubstituted oxiranes gave the 2,3,6-trisubstituted phenols with a skeleton reorganization [22]. The 1,2-deuterium shift of the alkynyl deuterium of d-Sle was indicative of mthenium vinylidene intermediates (Scheme 6.20).

The (R) allene 121 was obtained with high anti stereoselectivity in the reaction of (i )-(—)-l-trifluoroacetoxy-l-phenyl-2-propyne (120) with PhZnCl. 2-Alkynyloxiranes react smoothly with alkynyl, alkenyl and arylzinc reagents. Reaction of 2-methyl-2-(l-propynyl)oxirane (122) with vinylzinc chloride (123) yields 2,4-dimethyl-2,3,5-hexatrien-l-ol (124) [31],... 

Various metal acetylides are used for smooth coupling with propargylic halides and acetates. 2,3-Alkadien-5-yn-l -ols are obtained by the reaction of 2-(l -alkynyl)oxiranes [28,29], As a synthetic application, the unstable 2,3-octadiene-5,7-diyn-l-ol (136), a fungus metabolite, has been synthesized by the coupling of 4-trimethylsilylbutadiy-nylzinc chloride (134) with 2-ethynyloxirane (135) followed by desilylation [31]. 

In the nucleophilic opening of oxiranes by silver acetylides (see Section 10.4), Koide et al. provided good evidence for transmetallation of silver acetylides to dichlorozirconocene leading to alkynyl zirconium species.98... 

Table 47 Trimethylgallium-catalyzed alkynylation of oxiranes. Reproduced with permission from CSJ...

The addition of carbon nucleophiles to alkynyl-substituted oxiranes has been reviewed <2002CUOC539>. The reaction between indoles and oxiranes occurs readily under catalysis using indium(iii) bromide <2002JOC5386>. A related process involves solid-state activation using silica gel to promote the reaction <2005JOC3490>, or... 

A number of substituents can be placed on the periphery of the vinyloxirane system. For example, extensively studied were alkynyl- and dienyl-oxiranes of the general structures represented by (138a) to... 

A pyrrolinium iodide has been obtained via the reaction of 2-methyl-2-alkynyl-oxirane with dimethylhydrazine (e.g., Eq. 203). ... 

Organoaluminium compounds have been utilized for alkynylation of alicyclic oxiranes in prostaglandin synthesis and for the preparations of m-alkenols (Eq. 252). ° ... 

Scheme 11.9 Allenylpalladium complex formation from 2-(l-alkynyl)oxiranes. 

Scheme 11-56 Reactions of various 2-(l-alkynyl)oxiranes with methyl acetoacetate.

Grignard reagent with alkynyl oxiranes 54 is also very regioselective toward the Sn2 product 55, and the syn-process is the sole process observed [Eq. (18)]. 

Alkynylation of oxiranes or oxetanes with lithium alkynides is effectively carried out in the presence of BF3 OEt2 at -78 C. The use of BF3 gives better results than TiCU, SnCU or AlCU. The reaction takes place stereospecifically with anti opening, and the attack generally occurs at the less hindered site. Several functional groups such as halogens, acetals or certain esters survive the reaction conditions (Scheme 16). 100-102... 

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