Alkynes Hept-2-ynes

Under optimized conditions, cycloisomerizations of a number of functionalized hept-l-en-6-ynes took place in good-to-excellent yields (Table 9.3). Heteroatom substitution was tolerated both within the tether and on its periphery. Alkynyl silanes and selenides underwent rearrangement to provide cyclized products in moderate yield (entries 6 and 7). One example of seven-membered ring formation was reported (entry 5). Surprisingly, though, substitution was not tolerated on the alkene moiety of the reacting enyne. The authors surmize that steric congestion retards the desired [2 + 2]-cycloaddition reaction to the point that side reactions, such as alkyne dimerization, become dominant. 

The cationic binuclear complex [(Mes3PAu)2Cl]BF4 has been found to catalyse the reaction of 2-methyl- or 2-pentyl-furan (78) with phenylacetylene, pent-l-yne, or hept-l-yne (79) to afford the products of a twofold hydroarylation of the alkyne (80).120... 

The corresponding alkyne bicyclo[2.2.1]hept-2-yne might behave like a wc-dicarbcnc that first yields carbene 46 via 1,3-CH insertion, which then forms an intermolecular cyclopropanation product. However, this pathway was not suggested. See (a) Laird, D.W. and Gilbert, J.C. (2001). J. Am. Chem. Soc. 123, 6704-6705 (b) Laird, D.W. and Gilbert, J.C. (2001). Chem. Eng. News 79 (28), 41... 

Enynes in which three or four atoms separate the double and triple bonds cyclize upon complexation to Co2(CO)g and subsequent heating to give bicyclic enones (equation 52). With the exception of slightly elevated temperatures the conditions required are no different than those of the stoichiometric procedure described earlier for reactive substrates in intermolecular Pauson-Khand reactions. The intramolecular cycloaddition cannot in general be carried out under catalytic conditions. Hex-l-en-5-yne, which would give a four-membered ring upon intramolecular cycloaddition, instead undergoes alkyne trimerization exclusively.3 The most extensively studied systems are those derived from hept-l-en-6-yne, as the products, bicyclo[3.3.0]oct-l-en-3-ones, are useful in the synthesis of numerous cyclopentane-based polycy-clics. 

Finally, one may note the curious behaviour of alkynes. If Mo(CO)6/non-4-yne is irradiated at room temperature and an excess of 3-chlorophenol then added, there is rapid metathesis to give oct-4-yne and dec-5-yne with nearly 100% selectivity (Mortreux 1977). In contrast, W(CO)6/CCl4//iv (350 ran) induces polymerization of hept-2-yne while causing metathesis of pent-2-ene present in the same reaction mixture (Stockel 1978). The difference in behaviour of the two systems presumably lies in the ability of Mo(CO)6/non-4-yne// v to generate a metal carbyne on addition of the phenol, whereas W(CO)6/CCl4/Av gives only a metal carbene. Photoassisted polymerization of terminal alkynes takes place with WCV/iv in hydrocarbon solutions (Landon 1985) photocatalyzed polymerization of substituted alkynes is induced by W(CO)6/SnCl4// v (Tamura 1994). For related systems, see Ch. 10. 

The species [Ir(cod)(PPh3)(pz)] or [Ir(cod)(pz)]2 in the presence of PPhj (pz = pyrazolato) dissolves in acetone to yield catalytic solutions which partially hydroformylate and hydrogenate alkynes and alkenes. Results were reported for the hydroformylation of hept-2-yne. The hydrosilylation of styrene by [Si(Cl)2(H)Me] is catalyzed by complexes of the type [ML,L , ] (M = Ir, Co, Ni, Ru, Rh, Os, Pd, Pt L = halide, NO2 , SCN L = DMSO, Et2SO, Et2S, NHj). The catalytic activity and regioselectivity of these catalysts have been examined after immobilization on AVI 7X8 or KU 2X8 anion exchangers. ... 

The intramolecular Diels-Alder cycloadditions of 1-aminobenzofurans provide a simple synthesis of benzo[/r]quinolines. A-Acetyl-2-azetine undergoes facile 4-1-2-cycloaddition with cyclopentadiene, 5,5-dimethoxy-1,2,3,4-tetrachlorocyclopentadiene, hexachloropentadiene, and diphenylisobenzofuran to produce exclusively endo-cyc o-adducts. The highly strained cyclic alkyne bicyclo[2.2.1]hept-2-en-5-yne (108), prepared from the heptavalent iodine precursor (107), has been trapped using 1,3-diphenylisobenzofuran to yield the adduct (109) (Scheme 41). The reaction of sodium dinitroxytrioxide (110) with 1,3-diphenylisobenzofuran gives an initial 4-1-2-cycloadduct (111), which rearranges to the final product (112) (Scheme 42). " The... 

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