Science of Synthesis

Mikami, K.; Matsumoto, Y.; Shiono, T., Science of Synthesis, (2003) 2, 530.

Propargyl- and allenyltitanium complexes ‌146‌ and ‌147‌ react with electrophiles such as ketones, aldehydes,[‌282‌] imines,[‌289‌] trialkylchlorostannanes,[‌290‌] azodicarboxylates,[‌291‌] bromine, thiocyanates, and water[‌292‌] (‌Scheme 78‌). The reaction with water proceeds through the coordination of the oxygen atom to titanium, followed by electrophilic cleavage by an SE2′-type reaction. The halogenolysis proceeds via a halonium cation intermediate, which subsequently undergoes SE2′ anti-halodemetalation. Optically active propargyl phosphates also react with more than 97% chirality transfer with divalent titanium complex ‌142‌ to afford optically active allenyltitanium complexes. However, the same reaction with optically active propargyl carbonates gives the opposite enantiomer, via a transition state in which the carbonyl oxygen atom or propargyl carbonate group is coordinated to titanium.[‌290‌] The allenyltitaniums thus prepared are stable to racemization up to at least room temperature.

‌Meeeee 88‌ Meeeeeeee ee Meeeeeee(MM)–Meeeeeeee eee –Meeeeee Meeeeeeee eeee ­Meeeeeeeeeeee[‌888‌,‌888‌–‌888‌]

Meeeeeeeeeee Meeeeeeee

Meeeeeee(8-eeeeeeeee-8-eeee)eeeeeeee (‌888‌, M8 = M8 = Me); Meeeeee Meeeeeeee:[‌888‌]

M eeee ee 8.88 M eMeMeMe (8.8 eM, 8.8 eeee) ee Me8M eee eeeee eeeeeeee ee e eeee ee eeeee 8-eeeeeeee-8-eeeeee (888 ee, 8.8 eeee) eee [Me(MeMe)8] (888 μM, 8.8 eeee) ee Me8M (88 eM) ee −88°M. Mee eeeeeeeee eeeee eeeeee eeee eee eeeeeee eee 8 e ee −88°M. Meeeee eeee eeeeee, eee eeeee ee eee eeee eeeeeee eeee eeeeee ee eee-eeeee. Mee eeee eee eeeeee ee −88°M, eee Me8MeMe (888 μM, 8.8 eeee) eee eeeee; eee eeeeeee eee eeee eeeeeeeee eeeeee ee 8°M eeee 8 e. Mee eeeeeee eee eeeeeeee eeee eee. ee MeMMM8 eee eeeeeeeee eeee eeeeeee. Mee eeeeeeee eeeeeee eeeeee eeee eeeee (Me8MM8) eee eeeeeeeeeeee ee eeeee. Mee eeeeeee eee eeeeeeeeeeeeeee (eeeeee eee, eeeee eeeeee, eeee Me8M) ee eeee ee eee, eeeee eeeeeeeee ee e eeeeeee ee eeeeeee ‌888‌ (M8 = M8 = Me) eee eeeeeeee(8-eeeeeeeeee-8,8-eeeeee)eeeeeeee (88:8); eeeee eeeee: 88%.

References