Reductive umpolung reactions with low-valent titanium catalysts.

The coupling of similarly polarized carbon fragments can be achieved by a reductive umpolung strategy. This gives access to compounds with functional groups in even bond distances, which are difficult to synthesize by other means. Low-valent titanium catalysts enable such couplings under mild conditions. This account covers the recent progress on this topic with a focus on the development of cross-selective coupling reactions and stereoselective examples.