Strained cyclic alkynes

Strained Cyclic Alkynes, and Strained Cyclic Cumulenes. 

Strained cyclic alkynes are the most powerful olefinic 7r-donors for gold(i) centers. This has been demonstrated for the cycloheptynes shown in Scheme 80. The Au-C distances are in the range from 2.050 to 2.100 A.318 There is also evidence for the coordination of AuCl to Me3Si-C=C-SiMe3, but no details are available.319... 

Arynes, Strained Cyclic Alkynes, and Strained Cyclic Cumulenes. .. 42 147... 

Normally, a discussion of strained cyclic alkynes (which is the focus of this section) would not include rings with more than seven or eight members.1-3 However, a notable exception is [2.2]paracyclophane-l-yne (277), formally... 

Furthermore, the successful [3+2+1] cycloaddition of alkynes bearing a cyclopropane ring and a carbene complex unit has been reported. These benzannulations result in the formation of bimetallic naphthohydroquinone chromium tricarbonyl complexes [48]. Additionally, (non-strained) cyclic alkynes are potent reaction partners in the cycloaddition of chromium carbene complexes [49]. 

The high reactivity of propargylic halides toward nucleophiles allows the preparation of some rather strained cyclic alkynes and especially dialkynes, in surprisingly simple ways. Thus, the ten-membered ring 22 can be prepared in one step from methylamine and 1,4-dibromo-2-butyne (20), [12] (Scheme 8-2). 

Heteronuclear addition reactions to alkynes usually produce the corresponding trans-alkene derivatives. However, in the case of strained cyclic alkynes, these would be even more heavily strained than the starting alkyne. Thus, in most reactions, cis-products are observed. The initial addition of the electrophile may, however, still proceed in an anh -manner, as was shown by Krebs et al. [1 b] for the reaction of a cycloheptyne derivative with trichloromethylsulfenyl chloride (Scheme 8-21). This reaction produced the first seven-membered rm s-cycloalkene derivative to be isolable at room temperature. 

Highly strained cyclic alkynes can be stabilized by complexing them with metal compounds [1 b, c 75, 76]. Thus, even reactions with elusive species such as cyclohexyne are possible, as exemplified in Scheme 8-26 [78]. 

Bennett MA, Schwemlein HP (1989) Angew Chem Int Ed Engl 28 1296 Buchwald SL, Broene RD (1995) In Abel EW, Stone EGA, Wilkinson G (eds) Hegedus LH (vol ed) Comprehensive organometallic chemistry 11, vol 12. Pergamon, Oxford, p 771 Jones WM,Klosin J (1998) Transition metal complexes of arynes, strained cyclic alkynes, and strained cyclic cumulenes. In Stone EGA, West R (eds) Adv Organomet Chem, vol 42. Academic, San Diego, p 147... 

Reaction (47) leading to an all carbon three membered ring involving however a double bond is less well known except for the addition of aryl-isocyanides to electron rich or strained cyclic alkynes [71],... 

Gomprehensive reviews of the chemistry of heavy allenes and cumulenes, heteroaldehyde, heteroketone, phosphaalkene " " and 77 -ketenyl (77 -G(PPh3)=GO) " complexes, which include platinum complexes, have been published. A review of transition metal complexes of arynes, strained cyclic alkynes, and strained cyclic cumulenes also includes information relative to this section. " ... 

Several reviews of the chemistry of strained cyclic alkynes and arynes and otiho-ztene cyclynes, " which include synthesis, structure, and reactivity of platinum complexes, have also appeared. The behavior of 1,4-enynes in the presence of transition metals has been reviewed. ... 

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... 

Jones, William M., and Klosin, Jerzy, Transition-Meted Complexes of Arynes, Strained Cyclic Alkynes, and Strained Cyclic Cumulenes. . . Joseph P. Morrall, Gulliver T. Dalton, Mark G. Humphrey and Marek Samoc, Organotransition Metal Complexes for Nonlinear Optics.. . . Jxmg, IL Nam, see Yoo, Bok Ryul... 

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