Alkynes and Allenes

Nonstabilized carbonyl ylides (41) prepared by reaction of a-iodosilyl ethers with Smlj, can be trapped with various alkenes, alkynes and allenes to form furans of type 42, 43, and 44... 

Organometallic complexes of the /-elements have been reported that will perform both intra-and intermolecular hydroamination reactions of alkenes and alkynes, although these lie outside of the scope of this review.149-155 Early transition metal catalysts are not very common, although a number of organometallic systems exist.156-158 In these and other cases, the intermediacy of a metal imido complex LnM=NR was proposed.159,160 Such a species has recently been isolated (53) and used as a direct catalyst precursor for N-H addition to alkynes and allenes (Scheme 35).161,162... 

Intramolecular nucleophilic additions by nitrogen functional groups onto pendant alkynes and allenes represent an important class of type la approaches to functionalized pyrroles. A platinum-catalyzed (PtCl4) cyclization of homopropargyl azides provided an entry to 2,5-disubstituted pyrroles and 4,5,6,7-tetrahydroindoles (fused pyrroles) <06OL5349>. 

Rhodium complexes catalyze hydrosilylation-cyclization of 1,6-allenynes in the presence of (MeO SiH.77 To avoid complex product distributions, the use of substrates possessing fully substituted alkyne and allene termini is imperative. As shown in the cyclization of 1,6-allenyne 62a, the regiochemistry of silane incorporation differs from that observed in the rhodium-catalyzed hydrosilylation-cyclization of 1,6-enynes (see Section 10.10.2.3.2). For allenyne substrates, allene silylation occurs in preference to alkyne silylation (Scheme 40). 

Carbostannation of alkynes and allenes has recently been developed and provides an important new route to stannylalkenes (Equation (35)). 

Scheme 9.1 Synthesis of aiienyimetai compounds from propargylic halides, alkynes, and allenes.

Scheme 23 Pd-catalyzed carbonylation of iodophenol with alkynes and allenes...

Regioselective stannylcupration of terminal alkynes and allenes, followed by quenching of the cuprate intermediate with ethylene oxide, provides a facile synthesis of cyclobutene and alkylidine cyclobutane derivatives, respectively (Scheme 3.23) [15c]. A number of total syntheses have exploited regioselective stannylcup-... 

The cationic gold complex with CAAC ligand 29 can also catalyze the unprecedented hydroamination reaction of alkynes and allenes using ammonia [59, 60]. It was also demonstrated that it can catalyze the simple hydroamination reaction. It... 

Boron trifluoride etherate, 43 of alkynes and allenes Lithium 3-aminopropylamide, 160 of unsaturated carbonyl compounds Alumina, 217... 

R2 = allylic, PhCH2, CH2C=CH (alkyne and allene product) TL 36 6495 (1995)... 

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