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Please login to access the full content or check if you have access via Method 9: Reactions of Bis(isopropoxy)titanium(IV)–Propargyl or –Allenyl Complexes with Electrophiles

DOI: 10.1055/sos-SD-002-00576

Mikami, K.; Matsumoto, Y.; Shiono, T.Science of Synthesis, (20032530.

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.

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