Why does LiAlH4 reduce the double bond of cinnamaldehyde, whereas NaBH4 does not?

I read an answer [here](https://chemistry.stackexchange.com/questions/6977/why-does-nabh4-affect-double-bonds-while-lialh4-does-not) about why $\ce{LiAlH\_4}$ does not reduce conjugated double bonds, and that $\ce{NaBH\_4}$ does. But in the case of cinnamaldehyde, $\ce{LiAlH\_4}$ reduces the conjugated double bond and $\ce{NaBH\_4}$ does not. Why is it so?


Citation for $\ce{LiAlH\_4}$: [Quora](https://www.quora.com/In-which-cases-does-LiAlH4-reduce-double-bond-between-two-carbon-atoms/answer/Sharad-Pratap-Singh-8)


Citation for $\ce{NaBH\_4}$:


[![NaBH4 with cinnamaldehyde](https://i.stack.imgur.com/jZd2M.png)](https://i.stack.imgur.com/jZd2M.png)


[Image Source](http://www.art-xy.com/2009/11/lab-report-on-reductive-amination.html)




Cinnamaldehyde (**1**) does not undergo 1,4-reduction but rather 1,2-reduction with LiAlH4. The product of the reduction is 3-phenylpropan-1-ol (**2**). If conjugate addition were to occur, enolate **3** would be produced (stable to the reductant; enolates can be prepared to protect ketones from this reductant) and aldehyde **4** would be expected, as long as the aqueous workup were to destroy the reductant before any enolate **3** could be protonated.


All of this aside, the answer was provided experimentally in 1954.1 Reduction occurs 1,2 to afford the aluminate salt of cinnamyl alcohol **5**. This species undergoes hydroalumination of the double bond by a presumed intramolecular process to give alkyl aluminate **6**. This cyclic aluminate was deuterated (D2O) at the benzylic position to provide **9**. In addition, trapping of **6** with benzophenone afforded diol **7** in >80% yield! Reduction of cinnamaldehyde with LiAlD4 and aqueous workup would be expected to give dideuterio 3-phenylpropan-1-ol (**8**).  
  

Sodium borohydride reduces cinnamaldehyde via 1,2-reduction in hydroxylic solvent to cinnamyl alcohol in 97% yield.2 The intermediate alkoxyborane (Cf.; structure **5**) either is incapable of reacting with the double as the aluminate does or the alkoxyborane rapidly exchanges with solvent.


[![enter image description here](https://i.stack.imgur.com/5y4ZO.jpg)](https://i.stack.imgur.com/5y4ZO.jpg)


1) Dornow, A., Winter, G., Vissering, W. *Chemische Berichte*, **1954**, *87*, 629.  

2) Chaikin, S.W., Brown, W.G., *J. Am. Chem. Soc.*, **1949**, *71*, 122.


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