Identify the major product B in the following reaction sequence:

Step-by-step solution

The starting material is a bicyclo[3.3.0]octane derivative, drawn with the fused bond horizontally. The top vertex corresponds to the C3 position with an aldehyde ( - CHO ) group, the bottom vertex is the C7 position with a ketone ( = O ) group, and the right bridgehead carbon has a methyl ( - CH ₃ ) group. In the first step, the reaction with ethylene glycol ( CH ₂ OH - CH ₂ OH ) and dry HCl selectively protects the more reactive aldehyde group as a cyclic acetal. The ketone group remains unreacted because aldehyd