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SolutionsPreparation

1. From alkene to alkyne

Plan the following transformation:

Transformation of vinylcyclobutane into ethynylcyclobutane in two steps
Addition of Br₂ in CCl₄ to give the vicinal dibromide and double elimination of HBr with a strong base

The second elimination, from the vinyl bromide, is harder and needs a very strong base, such as NaNH2.

2. Alkylation

How would you prepare 1-phenyl-2-butyne, C6H5CH2C≡CCH3, from propyne?

1) NaNH2, NH3; 2) benzyl bromide, C6H5CH2Br (SN2 nucleophilic substitution).

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