CARBON HOMOLOGATION OF 1-ALKYNES USING ALKOXYMETHYL ESTERS MEDIATED BY DICHLOROBIS(TRIFLUOROMETHANESULFONATO)TITANIUM(IV)

Various 1-alkynes were converted to 1-alkoxy-3-chloro-2-alkenes using alkoxymethyl esters and dichlorobis(trifluoromethanesulfonato)titanium (IV) [TiCl2(OTf)(2), titanium(IV) bis(triflate)]. This carbon homologa tion proceeded in the case of not only simple 1-alkynes but also for s everal 3- or 4-dimethylcarbamoyloxy-, 5-benzoyloxy-, 5-phenoxycarbonyl oxy-, and 5-methoxycarbonyloxy-1-alkynes. Among them, 3- and 4-dimethy lcarbamoyloxy-1-butynes underwent the reaction without loss of their f unctionalities compared with the other oxy substrates. The stereoselec tivity was Z predominant, especially in the case of the above mentione d 3-, 4-, and 5-oxy substituted 1-alkynes. Addition of TiCl4 to this s ystem was somewhat effective for enhancing the Z ratios. Titanium(IV) bis(triflate) was the only effective catalyst among several Lewis acid s such as AlCl3, TiCl4, SnCl4, ZnCl2, and Sn(OTf)(2). As a functionali zation of the obtained vinyl chloride, chloro-4-dimethylcarbamoyloxyl- 1-methoxy-2-pentene was converted into the corresponding ketone using Hg(OCOCF3)(2).