Propargyl iodides

Propargyl alcohol gives a 70 30 mixture of iodoallene and propargyl iodide. For... 

Note Propargyl ahlornde gives comparable amounts of propargyl iodide and iodoallene. Propargyl tosylate will probably yield a product that is free from the allene. 

Various halogenating agents have been used to replace hydroxyl with chlorine or bromine. Phosphoms trihaUdes, especially in the presence of pyridine, are particularly suitable (17,18). Propargyl iodide is easily prepared from propargyl bromide by halogen exchange (19). 

As shown in Scheme 7-21, an equimolar mixture of dimethylzinc and the coside chain vinyl lithium is treated sequentially with siloxyl-2-cyclopentenone and the propargylic iodide in the presence of HMPA. The desired product 79 is formed with 71% yield.12 The acetylenic product is a common intermediate for the general synthesis of naturally occurring PGs. 

A related method of preparation involves the oxidative addition of a tin(II) salt to propargylic iodides, which yield mixtures of allenyl- and propargyltin halides on treatment with SnCl2 in DMF-DMI (l,3-dimethylimidazol-2-one) (Eq. 9.75) [68], These intermediates react in situ with aldehydes to afford mixtures of propargylic and allenic carbinols via a cyclic SE2 process (Eqs. 9.76 and 9.77). As explained in the Introduction, the ratio of these two products reflects the relative transition-state energies of the addition reactions. 

Cyanomethyl)zinc bromide, BrZnCH2CN (1). The reagent converts alkyl, ally lie, or propargylic iodides in the presence of HMPT to nitriles. The reaction is particularly useful for synthesis of y,5-unsaturated nitriles.5 Example ... 

Dimerization under mild conditions has been achieved for the fluorinated propargyl iodide 5 with zinc/acetic anhydride in dichloromethane to give 3,3,4,4-tetrafluoro-l, 6-diphenylhexa-1, .5-diyne (6) in 67 % yield. ... 

Similar treatment of TMS propargyl iodide affords a mixture of allenic and pro-pargylic adducts (Table 48). The regioselectivity is strongly solvent-dependent. Allenic adducts predominate in MeCN-DMSO whereas in 1,2-dimethoxyethane (DME) the propargylic adducts are the major products. In these additions the structure of the aldehyde plays a minor role. 

Propargyl radical was produced by vacuum pyrolysis (900-1050°C, 10" -10 Torr) of propargyl iodide or of dipropargyl oxalate (Korolev et al., 1989) and it was frozen into an argon matrix at 12 K (15). Twelve bands were observed in the matrix IR spectrum of the C3H3 radical [only three bands were recorded earlier (Jacox and Milligan, 1974) for this radical] 3307, 3111, 3026, 2080, 1440, 1369, 1061, 1017, 686, 618, 532, 482 cm . Based on the experimental IR spectrum, a normal coordinate analysis has been carried out and a valence force field calculated (Table 6). Stretching frequencies of the carbon skeleton [v(C=C) 2080 cm and p(C—C)... 

This methodology has been extended to 4-alkynyl-4-(propargyloxy)cyclobutcnones,2 formed by addition of lithium acetylides to dimethyl squarate (3) followed by treatment of the 1,2-adducts with propargyl iodides. These products (4) when heated at 135° rearrange to methylenebcnzofurans (5), which isomcrizc in an acidic medium to benzofurans (6). 

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