Sila-alkynes

Interaction of sila-alkynes with excess iodosobenzene 4 in the presence of excess triethylox-onium tetrafluoroborate in dichloromethane at room temperature leads [27] to the formation of alkynyliodonium tetrafluoroboiates 12 [Eq. (4)]. A variation of this procedure employs Et20 BF3 followed by treatment with aqueous NaBp4 [Eq. (5)] [27, 28]. To date only alkyl-and aryl-substituted homologs, along with the silyl ethynyliodonium tetrafluoroborates, 12, have been reported via these procedures. 

Reaction of butadiynyltributylstannanes 25 with 7 in dichloromethane at — 40 °C results in the corresponding l,3-diynyl(phenyl)iodonium triflates 26 [Eq. (13)] [36]. These novel iodonium salts represent a new type of functionalized, conjugated diyne as well as an interesting iodine(III) species. Iodonium salts bearing two alkynes as organic ligands are also known [37]. These species, 28, are prepared by the reaction of sila-alkynes with iodosyl triflate, 27 [Eq. (14)] [38]. 

The reaction of l,4-bis(trimethylsilyl)-l,3-butadiyne (174) with disilanes, followed by treatment with methylmagnesium bromide, produces i,l,4,4-tetra(-trimethylsilyl)-l,2,3-butatriene (175) as a major product[96]. The reaction of octaethyltetrasilylane (176) with DMAD proceeds by ring insertion to give the six-membered ring compounds 177 and 178[97], The l-sila-4-stannacyclohexa-2,5-diene 181 was obtained by a two-step reaction of two alkynes with the disilanylstannane 179 via the l-sila-2-stannacyclobutane 180[98],... 

The original Sonogashira reaction uses copper(l) iodide as a co-catalyst, which converts the alkyne in situ into a copper acetylide. In a subsequent transmeta-lation reaction, the copper is replaced by the palladium complex. The reaction mechanism, with respect to the catalytic cycle, largely corresponds to the Heck reaction.Besides the usual aryl and vinyl halides, i.e. bromides and iodides, trifluoromethanesulfonates (triflates) may be employed. The Sonogashira reaction is well-suited for the synthesis of unsymmetrical bis-2xy ethynes, e.g. 23, which can be prepared as outlined in the following scheme, in a one-pot reaction by applying the so-called sila-Sonogashira reaction ... 

Recently, Peterson-type reactions have been applied to the syntheses of transient and stable heavy element analogues of alkenes and alkynes. Transient and isolable silaethenes 207331 were prepared by the sila-Peterson reactions121,321,332 340. Similarly to the original Peterson reactions341,342, the sila-Peterson reactions were found to involve a 1,3-silyl migration from silicon to oxygen (equation 135)321. 

The disylanylstannane 635 adds terminal alkynes regio- and stereoselectively to form (Z)-alkenes 636, which undergo a tetrakis(triphenylphosphine)palladium-catalysed reaction with phenylacetylene to give 1 -sila-4-stannacyclohexa-2,5-dienes 637. 1,4-Dithianes 639 ( = 1) and 1,4-dithiepanes 639 n = 2) are obtained by the azoisobutyronitrile - induced homolytic cycloaddition of alkynes R C=CR (R = Pr, Bu or CMe20H R = H or Pr) to the dithols 63836 7a b. 

---