Major product of Friedel-Crafts acylation of anisole with ethanoyl chloride is 4-Methoxyacetophenone.

Explanation:
The Friedel-Crafts acylation reaction involves the reaction of an aromatic compound with an acyl chloride (or acid anhydride) in the presence of a Lewis acid catalyst, such as aluminum chloride (AlCl3). In this reaction, the acyl group (-COCH3) from ethanoyl chloride is transferred to the benzene ring of anisole to form a new carbon-carbon bond.

The reaction mechanism proceeds as follows:

1) Formation of a complex: The Lewis acid catalyst, AlCl3, reacts with the acyl chloride to form a complex, which activates the acyl chloride for attack by the aromatic ring.

2) Electrophilic attack: The complex reacts with the aromatic ring of anisole, which acts as a nucleophile, leading to the formation of a carbocation intermediate. The nucleophilic attack occurs at the ortho and para positions of the anisole ring.

3) Rearrangement: The carbocation intermediate can undergo rearrangements to form more stable carbocation intermediates.

4) Deprotonation: The carbocation intermediate is then deprotonated by a molecule of AlCl4-, which acts as a base, to give the final product.

In the case of Friedel-Crafts acylation of anisole with ethanoyl chloride, the major product formed is 4-Methoxyacetophenone. This is because the acyl group from ethanoyl chloride prefers to attach at the para position (opposite to the methoxy group) of the anisole ring. The para position is more favorable due to the steric hindrance caused by the methoxy group at the ortho position.

Hence, the major product of Friedel-Crafts acylation of anisole with ethanoyl chloride is 4-Methoxyacetophenone (option D).