Direct geminal dimethylation of ketones and exhaustive methylation of carboxylic acid chlorides using dichlorodimethyltitanium

The reaction of ketones with an excess of (CH 3 ) 2 TiCl 2 ( 6 ) leads to the replacement of the carbonyl oxygen atom by two methyl groups. This mild method of direct geminal dimethylation involves Grignard‐type addition followed by formation of tertiary carbocations which are captured by methyltitanium species. Additional functional groups such as primary alkyl chlorides, thioethers, aromatics, ethers, and esters are tolerated, but not thioketals. The procedure has been applied to the synthesis of (±)‐cuparene ( 44 ). Similarly, carboxylic acid chlorides are converted to tert ‐butyl derivatives.