# Reaction of alkyl bromide in presence of piperidine

What are the products of this reaction? I believe there'll be E2 elimination to give the products. Not sure. Help would be greatly appreciated.

The above is the product which I thought might be possible due to E2 elimination

In case there is carbocation formation, this might be the intermediate:

Could there be nucleophilic substitution?

• How likely is it that the secondary cation will rearrange to a more stable species? Apr 24 '18 at 16:16
• @Waylander I thought so, but given that reaction type isn't mentioned I wasn't sure about it. Also, Piperidine being a strong base might abstract Hydrogen for E2 Elimination Apr 24 '18 at 16:29
• Could the cyclopropane ring behave like a double bond, making this the analogue of an allyl bromide, and yielding R2NCH2CH2CH=CH-tBu by attack on a cyclopropyl CH2 and ring opening? Especially given the steric hindrance near the carbon bearing the leaving group. Apr 24 '18 at 16:51
• @user6376297 Won't that require a Carbocation formation? But a protic polar medium hasn't been mentioned Apr 24 '18 at 17:05

@User6376297 raised a question:

"Could the cyclopropane ring behave like a double bond, making this the analogue of an allyl bromide, and yielding $\ce{R2NCH2CH2CH=CH-tBu}$ by attack on a cyclopropyl $\ce{CH2}$ and ring opening?" Especially given the steric hindrance near the carbon bearing the leaving group.

Indeed, that is the process going on in this case when the reaction was taken place in piperidine either at refluxing conditions or at room temperature. When (1-bromo-2,2-dimethylpropyl)cyclopropane (the alkyl bromide in question) was reacted in refluxing piperidine, it has yielded $88\%$ of (E)-1-(5,5-dimethylhex-3-en-1-yl)piperidine as a major product, which corresponds to the homoallylic analogue of the well-known SN2 process observed with allylic halide.

In addition, $8\%$ of 1-(1-cyclopropyl-2,2-dimethylpropyl)piperidine was also yielded as a minor product (Ref. 1 & 2). The authors claimed the formation of the minor product was not compatible with simple SN2 displacement due to the great steric hindrance imposed by the neighboring $\ce{t-Bu}$ and cyclopropyl groups, but the tight ion-pair mechanism (not separated by solvent) may explain the presence of SN2 product very well.

The percent yields of SN2' and SN2 products for the reaction at $\pu{25^\circ C}$ had been $73\%$ and $8\%$, respectively.

References:

1. Reaction of amines with cyclopropylcarbinyl halides: SN2' or solvolysis?: J. Org. Chem., 1985, 50(24), 4815–4821 (https://doi.org/10.1021/jo00224a033).

2. Homoallylic substitution reaction of piperidine with 1-bromo-1-cyclopropylalkanes: Tetrahedron Lett., 1983, 24(46), 5031–5034 (https://doi.org/10.1016/S0040-4039(00)94033-4).