AUyl carbonates cleavage

The proposed mechanistic sequence is shown in Scheme 6.1. Because the reaction is carried out under an atmosphere of CO, carbonyl loss and addition are likely to be reversible in many of these species. For simplicity, deuterium is shown only in one ortho-aryl position so that its rearrangements can be followed. The proposed mechanism relies upon the isotopic preference for deuterium on carbon to account for the location of deuterium in the quinoline product. Commencing with the cleavage of the ortho-aryl C-D bond by Co2(CO)7 in an intramolecular complex, hydride is eliminated as DCo(CO)3 which then coordinates to and inserts into an aUyl C-C double bond. The preference for a primary Co-C bond over a secondary Co-C bond leads to deuterium incorporation selectively at the (3-position of the alkyl group to form the intermediate A. This insertion is reversible, but the isotopic... 

A double bond in alkenes is also known to initiate a-cleavage reactions. Upon ionization, the radical can reside on either carbon atom of the double bond, leading to formation of a resonance-stabilized aUyl cation ... 

Starting from oxygen-linked 1,3-dicarbonyl compounds (malonates or acetoacetates), Tietze and co-workers have demonstrated an allylic substitution at the a-position of varions snbstrates (aUyl acetates, carbonates, and chlorides). Under the conditions employed, bisalkylation was observed in all cases. Since the acetoacetates could be alkylated by hard electrophiles at the y-position, a broad spectrum of compounds might be obtained. The cleavage from the resin was performed using DIBAL-H to obtain the corresponding diols (Scheme 24). 

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