REACTION OF MU-OXOBIS[(TRIFLUOROMETHANESULFONATO)(PHENYL)IODINE(III)] WITH GROUP-14 PROPARGYL DERIVATIVES AND A PROPARGYL ETHER

The treatment of 4,4-dimethyl-l-(trimethylsilyl)-2-pentyne (4a) or 4,4-dimethyl-l-(tributylstannyl)-2-pentyne (4b) with mu-oxobis[(trifluoromethanesulfonato)(phenyl)iodine(III)] (2) gives 4,4-dimethyl-l-(2-iodophenyl)-2-pentyne (9). Deuterium labeling has confirmed that propargylation of 2 occurs ortho to the position originally occupied by the I(III). The addition of 2 equiv of 4a to 2 at -80-degrees-C results in 2 equiv each of 9, trimethylsilyl triflate (10), and tert-butyballene (11) and 1 equiv of hexamethyldisiloxane (12); in contrast, the addition of 2 equiv of 4b to 2 at -30-degrees-C results in 2 equiv each of 9 and tributylstannyl triflate (16). A mechanism that explains these product ratios is proposed. The reaction of 2-o,o'-d2 and 4b shows the negligible intramolecular kinetic isotope effect (0.99 +/- 0.01) expected for what is in effect a Claisen rearrangement. The addition of 2 to 2-butynyl (trimethylsilyl)methyl ether (20) affords the single product 21 resulting from anti addition and control of regiochemistry by the ether oxygen. Attempts to desilylate 21 to an allenyl triflate result in the regeneration of the propargyl ether 20.