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.

Alkylative carbocyclization reactions of omega-iodoalkynyl tosylates with alkynyllithium compounds to give products with incorporated iodine atoms are described. Slow addition of 2-(3-iodoprop-2-ynyloxy)ethyl tosylates to 1-alkynyllithium compounds in tetrahydrofuran at 40 degrees C followed by additional stirring at this temperature gives (Z)-3-(1-iodoprop-2-ynylidene)tetrahydrofurans stereoselectively in good to moderate yields. Under similar conditions at 0 degrees C, 4-iodobut-1-ynyl tosylates react with 1-alkynyllithium compounds to give (1-iodoprop-2-ynylidene)cyclopropanes. The carbocyclization reactions are proposed to proceed through a new carbenoid-chain process involving the exo cyclization of a lithium acetylide intermediate and the vinylic substitution of the resulting TsO,Li-cycloalkylidenecarbenoids (Ts=tosyl) by 1-alkynyllithium compounds.

In the presence of 1-hexynyllithium, 2-(2-propynyloxy)ethyl iodides undergo carbocyclization with 1-iodo-1-hexyne to afford 3-(diiodomethylene)tetrahydrofurans in an atom-economical manner with incorporation of the two iodine atoms from the substrates and the reagent.

2008 Furan derivatives R 0060 Carbocyclization Reaction of ω-Iodoand 1,ω-Diiodo-1-alkynes Without the Loss of Iodine Atoms Through a Carbenoid-Chain Process. -In the presence of lithium compounds, iodoalkynes undergo novel cycloisomerization to give synthetically important (iodomethylene)tetrahydrofurans. The synthesis of cyclopentane and tetrahydropyran analogues is also possible. -(HARADA*, T.; MURAMATSU, K.; MIZUNASHI, K.; KITANO, C.; IMAOKA, D.; FUJIWARA, T.; KATAOKA, H.; J.

Alkylative Carbocyclization of -Iodoalkynyl Tosylates with Alkynyllithium Compounds Through a Carbenoid-Chain Process Leading to (1-Iodoprop-2-ynylidene)tetrahydrofurans and -cyclopropanes. -(HARADA*, T.; IMAOKA, D.; KITANO, C.; KUSUKAWA, T.; Chem. Eur. J. 16 (2010) 30, 9164-9174, http://dx.doi.org/10.1002/chem.201001105 ; Dep. Chem. Mater. Technol., Kyoto Inst. Technol., Sakyo, Kyoto 606, Japan; Eng.) -Nuesgen 01-029