Why a doubly-fused cyclohexanone is formed instead of bridged cyclohexanone like product which would be more flexible (entropically-favoured)?
Also, the OH group not being at the bridgehead carbon unlike former compound, shouldn't it have a better chance of forming stable alkenone after dehydration as the preferred product formed in Robinson annulation? The following image elaborates my doubt.
As per the Baldwin rule for enolate, the enol-endo reaction and enol-exo reaction is favoured for both exo-tet and exo-trig for six/seven-membered chain (from the excerpt is provided as above image).
Both the alternatives follow six-membered exo-trig which is favoured according to above Baldwin rule. (Refer to the image where the carbon chain of both the alternatives is numbered.) The bridged-bicycle compound has 3 faces, where each face has a 6-membered ring when it was visualized through ChemDraw 3D. So, it seems both the alternatives as the product of Robinson annulation is favoured according to modified Baldwin rules.