Reactions with allenylsilanes titanium tetrachloride

The reactions of steiically encumbered allenylsilanes of structure type (66) with A -acyliminium ions generated by the titanium tetrachloride promot reaction of ethoxypyirolidinone product the nitrogen heterocycle (70), as depicted in Figure 13. In this reaction it is likely the lactam prc uct is generated by a pathway similar to that involved in the [3 + 2] cyclopentene aimelation. Thus, a regiospecific electro-... 

The reaction of trimethylsilylallenes with aldehydes and ketones in the presence of titanium tetrachloride provides a regiocontrolled route to homopropargylic alcohols of a variety of substitution types. Thus, the addition of 1-alkyl-substituted trimethylsilylallenes to carbonyl compounds furnishes the desired alkynes directly, whereas reactions involving allenylsilanes initially produce mixtures of alkynes... 

Synthesis of 1,3-Dibydrofurans. (f-Butyldimethylsilyl)-allenes combine with aldehydes to produce dihydrofurans (eq 10). In a typical reaction, the aldehyde and 1.1 equiv of titanium tetrachloride are premixed at —78 °C in methylene chloride for 10 min. The allenylsilane (1.2 equiv) is then added, and the reaction mixture is stirred in the cold for 15—45 min. 

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