Synthesis of derivatives of podocarpane-type diterpenoids through Diels-Alder cycloaddition and photo-decarbonylation from unmasked ortho-benzoquinone

Derivatives of podocarpane-type diterpenoids, including cassane-type, abietane-type and totarane-type diterpenoids, are either widely distributed natural products or common intermediates in synthetic and medicinal chemistry. Although unmasked ortho-benzoquinone has been used in [4+2] cycloadditions in sparse cases due to its multiple reactivity as diene, dienophile, heterodiene and heterodienophile, applications of this motif in cycloadditions of complex molecules are very rare. We report herein that this [4+2] process can be successfully extended to various polycyclic substrates, followed by a photo-decarbonylation, to generate versatile derivatives of podocarpane-type diterpenoids. Racemic synthesis of isolophanthins A & B and abietatrien-3β-ol was accomplished on the basis of this methodology.

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