Synthesis of α-Methylene-γ-butyrolactones by Rearrangements of Cyclopropylcarbinyl Substrates

α-Methylene-γ-hutvrolactones can be viewed as derivatives of homoallylic alcohols, potentially obtainable from rearrangements of cyclopropylcarbinyl derivatives. In order to test this concept, the cyclopropylcarbinyl derivatives 3a-7a were prepared. Acid-catalyzed rearrangements of 3a and 4a, solvolytic rearrangements of 5a, and AgC10⁴-induced rearrangements of 6a and 7a gave the α-methylene-γ-butyrolactone 10 in good yields. The unsaturated substrates 3b-6b were similarly prepared and shown to rearrange to o-methylene lactone 16, showing that a suitably placed double bond can direct the regiochemistry of these rearrangements. Lactone 16 has a double bond in a position characteristic of many naturally occurring lactones.