Ethers, allyl regiocontrol

The above reactions are one pot syntheses, can be used for double alkylation or hydroxyalkylation of alkenes in good (55-65 %) yield, and with outstanding regiocontrol (> 99 %). Diastereoehemical control in the formation of allylic alcohols and ethers has been shown to proceed with even better yields (up to 92 %) although the stereocontrol is somewhat decreased (95 5, highest as low as 67 33) due to the use of THF as a solvent which can influence the stereochemistry. These studies are important since the different reaction pathways can lead to both protected and unprotected alcohols. Such pathways are shown in Eq. 2.12... 

Allyl silanes react with a wide variety of electrophiles, rather like the ones that react with silyl enol ethers, provided they are activated, usually by a Lewis acid. Titanium tetrachloride is widely used but other successful Lewis acids include boron trifluoride, aluminium chloride, and trim ethyls ilyl tri-flate. Electrophiles include the humble proton generated from acetic add. The regiocontrol is complete. No reaction is observed at the other end of the allylic system. All our examples are on the allyl silane we prepared earlier in the chapter. 

The vinylogous thioacetal 33 was transformed into the a,(8-unsaturated ketone 34 upon CuOTf-mediated hydrolysis whereas the HgCl2-promoted reaction was less effective (Sch. 9) [27]. Similarly, vinyl sulfide 35, which bears an allylic alcohol, was converted into the aj3-unsaturated ketone 36 with complete regiocontrol [28]. This regioselectivity is not dependent upon the heteroatom because the vinyl ether 37 hydrolyzes to the aldehyde or ketone 38 [29]. 

Accordingly, the desired diol mono ethers 34 were synthesized in high yields with complete regiocontrol by the reaction of aldehydes with y-alkoxy allyl indium reagents (35 — 34a) (Scheme 9) (07OL953, 08T809). Acylation... 

---