Describe the alkyne you should start with and the reagents...

Key Concepts

Alkyne Structural Selection

This concept involves choosing the appropriate alkyne structure based on the desired carbon skeleton of the final product. When planning a synthesis, one must match the number and position of carbon atoms in the starting alkyne with those in the target alkene or alkane. In such problems, the internal or terminal placement of the triple bond is key to obtaining the correct regiochemistry after reduction.

Full Catalytic Hydrogenation

Full catalytic hydrogenation is the process of reducing an alkyne all the way to an alkane using catalysts such as palladium on carbon (Pd/C) under an atmosphere of hydrogen. This reagent system adds hydrogen across both pi bonds of the triple bond, yielding a saturated hydrocarbon. It is used when the goal is to synthesize alkane products, such as pentane in this context.

Selective Partial Hydrogenation (Syn Addition with Lindlar Catalyst)

Selective partial hydrogenation is a method used to reduce an alkyne only to an alkene, and it typically employs a poisoned catalyst, like the Lindlar catalyst, which allows for the addition of hydrogen in a syn fashion. This controlled addition produces cis alkenes, exemplified by cis-2-butene, by stopping the reduction reaction at the alkene stage without further conversion to the alkane.

Dissolving Metal Reduction (Anti Addition)

Dissolving metal reduction is a technique where an alkyne is reduced to a trans alkene by using a metal such as sodium in liquid ammonia. This reaction involves an anti addition of hydrogen, leading to a trans configuration of the carbon-carbon double bond. It is used when synthesis of a trans alkene, like trans-2-pentene, is required.

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