Carbocyclization reaction of omega-iodo- and 1,omega-diiodo-1-alkynes without the loss of iodine atoms through a carbenoid-chain process.
Atom-economical carbocyclization reactions of omega-iodo-1-alkynes and 1,omega-diiodo-1-alkynes to give products with incorporation of iodine atoms is described. Cycloisomerization of 2-(2-propynyloxy)ethyl iodides is initiated by a catalytic amount of LDA to give 3-(iodomethylene)tetrahydrofurans in high yields. Upon treatment of with a catalytic amount of 1-hexynyllithium, 1,omega-diiodo-1-alkynes efficiently undergo cycloisomerization to give (diiodomethylene)cycloalkanes. The diiodomethylene products are also obtained by iodine atom-transfer-type cyclization of omega-iodo-1-alkynes, using 1-iodo-1-hexyne as an external iodine atom source. Bromine atom-transfer and proton-transfer cyclization proceed as well by employing 1-bromo-1-octyne and 1-octyne, respectively. These reactions are proposed to proceed through a carbenoid-chain process involving exo-cyclization of the lithium acetylide intermediates to give Li,I-alkylidene carbenoids. It is shown that the exo-cyclization proceeded stereospecifically through inversion of the stereochemistry at the electrophilic carbon.
Department of Chemistry and Materials Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan.
Toshiro
T
Harada
Keiko
K
Muramatsu
Kenta
K
Mizunashi
Chie
C
Kitano
Daisuke
D
Imaoka
Takayuki
T
Fujiwara
Hiroshi
H
Kataoka
D000480:Alkynes / Q000138:chemical synthesis* / Q000737:chemistry*; D003500:Cyclization; D006838:Hydrocarbons / Q000737:chemistry; D007455:Iodine / Q000737:chemistry*; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D015394:Molecular Structure; D013237:Stereoisomerism
D000480:Alkynes; D006838:Hydrocarbons; C030011:carbene; D007455:Iodine; D008697:Methane