(a) Product — A cyclohexene fused to the anhydride. Both methyl groups end up cis on the ring, and both anhydride C=O groups are cis to each other (and endo with respect to the new ring).

(b) Stereospecificity — The Diels-Alder is concerted and suprafacial/suprafacial. Substituents that are cis on the diene stay cis in the product; substituents that are cis on the dienophile stay cis. (E,E) diene → both methyl substituents project on the same face → cis methyls.

(c) Kinetic effect of (Z,E) — A diene must reach the s-cis conformation to cyclize. (Z,E)-2,4-hexadiene has a methyl group blocking the s-cis rotation (severe A^1,3 strain), so the reactive conformation is destabilized and the rate drops.

Major product — Bicyclo[2.2.1]hept-2-ene (norbornene) with the –CO₂CH₃ group on the endo face (pointing toward the residual π bond, i.e., the same side as the bridging methylene).

FMO rationale — The dienophile's LUMO (lowered by the conjugated ester) interacts with the diene's HOMO. In the endo transition state, secondary (non-bonding) orbital overlap between the carbonyl π* and the diene's p-orbitals at C2/C3 stabilizes the TS by ~2–3 kcal/mol relative to the exo TS, so endo dominates kinetically. (Exo is often more thermodynamically stable but is not formed under typical conditions because Diels-Alder reactions at moderate temperature are kinetically controlled.)

(a) 6π electrocyclization — 6π electrocyclic; thermal → disrotatory; photochemical → conrotatory. Producing the cis 5,6-dimethyl product from the (E,Z,E) triene requires the disrotatory mode → thermal.

(b) [3,3]-Sigmatropic — The Cope rearrangement is allowed thermally through a chair-like 6-membered TS (6 electrons; suprafacial/suprafacial; aromatic Hückel TS). Thermal.

(c) [2+2] cycloaddition — 4 electrons. Thermally forbidden (would require antarafacial overlap). It is allowed photochemically, where excitation moves an electron into the π* and the s/s mode becomes Möbius-allowed.