Triflates, alkyl alkynation

Alkyl halides and triflates, alkane reduction, 27-32 alkyl halides, 28-31 a-halocarbonyl compounds, 31 vinyl and aryl halides and triflates, 32 Alkynes, alkane reduction, 45-46 Allyl acetates, reduction of, 51 Allyl alcohols ... 

The reaction takes advantage of the ease with which the functionalized alkynes used as starting material can be prepared and of the fact that a number of aryl and alkenyl halides or triflates, alkyl halides, and allyl esters can successfully be used as carbon donors. In the presence of carbon monoxide, a three-component process can take place, widening the scope of the reaction and providing a useful, straightforward entry into cyclization products incorporating a molecule of carbon monoxide. 

Haloalkynes (R—C=C—X) react with ArSnBu3 and Cul to give R—C= C—Ar. Acetylene reacts with two equivalents of iodobenzene, in the presence of a palladium catalyst and Cul, to give 1,2-diphenylethyne. 1-Trialkylsilyl alkynes react with 1-haloalkynes, in the presence of a CuCl catalyst, to give diynes and with aryl triflates to give 1-aryl alkynes. Alkynes couple with alkyl halides in the presence of Sml2/Sm. Alkynes react with hypervalent iodine compounds " and with reactive alkanes such as adamantane in the presence of AIBN. ... 

Benzyne, which is generated in situ from 2-(trimethylsilyl)phenyl triflate and KF, acts as an alkyne congener in distannation in the presence of palladium-/ r/-alkyl isocyanide complex.157 A variety of substituted benzyne derivatives inserts into the Sn-Sn bond to give l,2-bis(stannyl)benzenes (Equation (59)). The reaction fails to occur in the presence of other palladium catalysts such as Pd(PPh3)4. 

Likewise, alkynyliodonium tosylates can be coupled with dialkyl- and diphenyl cuprates 136 to afford the respective alkyl- and phenyl-substituted alkynes 137 (Scheme 56) [114]. An interesting example of this reaction involves the coupling of (trimethylsilyl)ethynyl iodonium triflate with cubyl cuprate generated in situ from iodocubane 138 [116]. 

Silver acetylides also reacted with epoxides yielding propargylic alcohols.27 As for related alkylations with silver acetylides (see Section 10.6.1), this reaction required zirconocene dichloride and catalytic amount of silver triflate. This method proved useful for both electron-rich and electron-deficient alkynes and compatible with various acid- and base-sensitive functional groups (Table 10.2). 

The preparation of alkoxy(l-alkynyl)carbene complexes (e.g., of compounds L M = C(OR1)—C=CR) mostly follows the two-step Fischer procedure,14 involving addition of a 1-lithio alkyne LiC=CR to a metal carbonyl L M(CO) to give a metal acylate L M=C(CTLi+) — C= CR14, which is subsequently alkylated with an oxonium salt [R130]BF4,15 an alkyl triflate R10S02C — CF3,16,22 or an alkyl fluorosulfonate R103SF16a,n ... 

The general synthetic scheme employing the reaction of 2-halo-substituted hetero-cyclics with the appropriate acetylenes in the presence of palladium catalyst affords the 2-alkyne-substituted heterocyclics, l-(2-benzothiazol)-2-phenylethyne was used followed by N-alkylation with methyl or propargyl triflate produces l-[2-(N-propargyl-benzothiazolium)]-2-phenylethyne. 

---