M syn1 key - synthesis practice problems PDF

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MultiStepSynthesis

OChemI

 How to approach multi-step synthesis: 1) Compare the final product (aka “target”) to the starting compound. What atoms need to added or removed? 2) What reactions are required to make the final product (target)? This is the organic compound in the middle. 3) What reaction will link the starting compound to the middle compound?  First,takeanatom“inventory”;inthisproblem,only2Hatomshavebeenremovedfromthestartingmaterial toformthetarget.But,wedon’thaveasinglereactionthatwouldperformthattransformation‐itwillrequire morethanonestep.Second:considerwhatreactionshavewestudiedtomakeanalkyne?

  SincetherearenoadditionalCstoadd,wewouldnotmaketheproductfromanotheralkyne.Thereactionwe needistheeliminationrxnfromadibromide:

 Thisrequires2molarequivalents(2eq.)ofstrongbasetoeliminateHBr,twotimes,toformthealkyne.  Now,theproblemhasbeensimplifiedtoasinglesteporganicreaction.Whatreagentsarerequiredtomakea dibromidefromanalkene?Thisisanadditionrxn,fromchap6:

 Inthiscase,wespecifythesolvent(CH2Cl2)toensurethatthedibromideisformed.Note,theuseofBr2/H2O wouldgiveabromohydrinandthatwouldnotworkinthissynthesis,sincethereisnowaytoeliminateHOBr. Thenextpagecontainsaproblemsetastheywouldappearinanexam.Tryyourhandatthese.

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MultiStepSynthesis

OChemI

 Texas two step: Each of these problems are two step synthesis of a product. In the boxes around the arrows, provide the reagents for the reaction; note that a second step [e.g. 1) BH3 then 2) NaOH/H2O2] may be required. In the rounded rectangle, draw the structure of the compound from the first reaction.  A:

B:

 C:

 D:

 E: Br H 3C

C

CH

H3C

C

CH2Br

Br



F:





MultiStepSynthesis

OChemI

 Texas two step: Each of these problems are two step synthesis of a product. In the boxes around the arrows, provide the reagents for the reaction; note that a second step [e.g. 1) BH3 then 2) NaOH/H2O2] may be required. In the rounded rectangle, draw the structure of the compound from the first reaction.  A:

B:

 C:

 D:

 E:

 F:

 ...