How does methyl vinyl ketone dimerise with heating?

[![enter image description here](https://i.stack.imgur.com/mZVKy.jpg)](https://i.stack.imgur.com/mZVKy.jpg)
**(A)** to **(B)** is simply reduction, tosylation followed by intramolecular reaction and removal of tosylate. However, I am not able to guess how dimerization will take place, seems similar to Rauhut–Currier reaction, but can't guess. Any hint?




The dimer of methyl vinyl ketone (**1**) is not shown in the choices in the question. The dimer is **A** shown below. It is a "tail-to-tail" dimer. Product **B** is an intramolecular ketal as a probable mixture of epimers. Compare with [this](https://pubs.acs.org/doi/pdf/10.1021/jo00406a009) paper.   
  



![](https://i.stack.imgur.com/KCBpp.jpg)


B. P. Mundy, et al., [*J. Org. Chem.*, **1978**, *43*, 2347.](https://pubs.acs.org/doi/pdf/10.1021/jo00406a009)


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