Allylation trifluoroacetaldehyde

The indium-mediated allylation of trifluoroacetaldehyde hydrate (R = H) or trifluoroacetaldehyde ethyl hemiacetal (R = Et) with an allyl bromide in water yielded a-trifluoromethylated alcohols (Eq. 8.56).135 Lanthanide triflate-promoted indium-mediated allylation of aminoaldehyde in aqueous media generated (i-airiinoalcohols stereoselectively.136 Indium-mediated intramolecular carbocyclization in aqueous media generated fused a-methylene-y-butyrolactones (Eq. 8.57).137 Forsythe and co-workers applied the indium-mediated allylation in the synthesis of an advanced intermediate for azaspiracids (Eq. 8.58).138 Other potentially reactive functionalities such as azide, enone, and ketone did not compete with aldehyde for the reaction with the in situ-generated organo-indium intermediate. 

A third approach to the preparation of allyl lluorovinyl ethers is the reaction of an allylic alcohol with trifluoroacetaldehyde, as illustrated by an alternative synthesis of 37a.17 Cinnamyl alcohol (47) forms with trifluoroacetaldehyde a hemiacetal, which is converted into bromide 48 via the mesy late. Reductive elimination affords 37a, which undergoes Claisen rearrangement within one hour in refluxing carbon tetrachloride to give 2,2-difluoro-3-phenylpent-4-enal (38a).17... 

Carbonyl compounds in certain protected forms such as gcm-diacetates" and hemiac-etals (e.g., trifluoroacetaldehyde ethyl hemiacetal ) also undergo allylation, giving in these cases homoallylic acetates and homoallyl alcohols, respectively. 

Likewise, indium trichloride as the catalyst in the presence of the stoichiometric amount of tin could replace indium as the promotor in the aqueous allylation of trifluoroacetaldehyde (Loh and Li, 1996). 

Fig. 8.14 Sn/InCb or In-mediated allylation of trifluoroacetaldehyde ethyl hemiacetal.

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