[6] In their report of the isolation and structural characterization of the natural product, Lee and co-worker proposed that the biosynthesis of torreyanic acid proceeded via an endo-selective [4+2] cycloaddition with a Diels–Alder dimerization of 2H-pyran monomers 2a and 2b.

[4] The proposed biosynthetic pathway is thought to involve: (a) an electrocyclic ring closure of 3, followed by (b) an enzymatic oxidation to furnish diastereomers 2a and 2b, and finally (c) a [4+2] cyclodimerization to generate torreyanic acid 1.

[7] The biomimetic synthesis of torreyanic acid involved the rapid conversion of aldehyde 3 to syn- and anti-pyrans 2a and 2b via an oxaelectrocyclization, with the pyrans existising as an equilibrium mixture.

[3] This total synthesis aimed to employ and confirm the Diels–Alder genesis proposed by Lee et al.[1] To synthesize the monomers required for Diels–Alder dimerization, 1,3-dioxane intermediate 4 was lithiated with BuLi, brominated with BrCF2CF2Br, and underwent acid hydrolysis to afford benzaldehyde 5.

Dimethoxyacetal 8 was furnished upon thermal Claisen rearrangement of 7, which afforded an unstable allyl phenol that directly underwent a hypervalent iodine oxidation with PhI(OAc)2 in methanol.

Intermediate 11 underwent a Stille vinylation with (E)-tributyl-1-heptenyl stannane, subsequently subjected to TBAF/AcOH for silyl removal and acetal hydrolysis to afford quinone epoxide 12.