Vinyl Ether Protecting Group

Silyl ethers are usually used as protecting groups for alcohols in organic synthesis.

Vinyl ether protecting group. A readily recyclable fluorous alkoxy ethyl ether protecting group has been developed that allows for simple purification of small to medium sized organic molecules by liquid liquid extraction with fc 72 organic aqueous solvents. This step is called deprotection. The general structure is r 1 r 2 r 3 si o r 4 where r 4 is an alkyl group or an aryl group. Etoch ch 2 roh etoch or ch 3.

The step to form the protected intermediate and a deprotection once the. Silyl ethers are a group of chemical compounds which contain a silicon atom covalently bonded to an alkoxy group. During efforts to employ a claisen rearrangement in the synthesis of a complex nucleoside a highly functionalized protected vinyl ether was required as a key intermediate. After the step involving the hydride is complete the acetal is removed by reacting it with an aqueous acid giving back the original carbonyl.

The super silyl group allows for the construction of β hydroxy aldehydes for a broad range of aldehydes providing 1 1 adducts in high yield. With catalytic amounts of acids ethyl vinyl ether adds to alcohols to give the mixed acetal. The allyl group is a commonly used protecting group for alcohols with relative stability towards both acidic and basic conditions that permits orthogonal protection strategies. The precursor vinyl ether 3 can be prepared in large quantity in a straightforward two step reaction sequence.

The acetal is then called a protecting group for the carbonyl. Protecting an amine as a carbamate therefore enables other functional groups to undergo selective reactions with electrophiles whereby the carbamate protected amino group is left intact. Isomerization to the more labile enol ether employing ko t bu with subsequent mild acidic hydrolysis is one of the most common deprotection methods. The polymers formed have a ketone end group e g 19 scheme 9 functionality can be introduced on z or r to modify reactivity or to tailor the end groups as in the examples 20 22.

However two additional synthetic steps are needed to achieve this protection. This alcohol protection reaction is akin to the behavior of dihydropyran. 1 when a propionaldehyde derived super silyl enol ether was used syn selectivity was observed scheme 1 table 1.