The major product A and the byproducts B formed in the following reaction are

Concept:

→ The Corey–Winter olefin synthesis (also known as Corey–Winter–Eastwood olefination) is a series of chemical reactions for converting 1,2-diols into olefins.

→ The reaction mechanism involves the formation of a cyclic thiocarbonate from the diol and thiophosgene.

→ The second step involves treatment with trimethyl phosphite, which attacks the sulfur atom, producing S=P(OMe)3 (driven by the formation of a strong P=S double bond) and leaving a carbene. This carbene collapses with loss of carbon dioxide to give the olefin.

Mechanism:

Conclusion:
The correct answer is option 1.