lecture 16 (ch 7) - Organic Lecture Series CH 310/318 M...

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Organic Lecture Series 1 CH 310/318 M LECTURE 16 Textbook Assignment: Chapter 7- Cont’d Today’s Topics: Alkynes Alkynes -reactions reactions Notice & Announcements: Exam II: Grading in Progress Organic Lecture Series 2 Alkynes Alkynes Chapter 7 Chapter 7
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Organic Lecture Series 3 • Treatment of an alkyne with hydrogen in the presence of a transition metal catalyst, most commonly Pd, Pt, or Ni, converts the alkyne to an alkane. 2-Butyne Butane + CH 3 C CCH 3 Pd, Pt, or Ni 2H 2 3 2 2 3 3 atm Reduction Reduction No selectivity No selectivity -complete reduction!! complete reduction!! Organic Lecture Series 4 • With the Lindlar catalyst, reduction stops at addition of one mole of H 2 . This reduction shows syn stereoselectivity. 3 3 H 2 CC 3 H 3 C HH Lin dlar catalyst cis- 2-Butene + 2-Butyne Reduction Reduction Pt on CaCO Pt on CaCO 3
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Organic Lecture Series Hydroboration Hydroboration - Protonolysis Protonolysis • Addition of borane to an internal alkyne gives a trialkenylborane. – Addition is syn stereoselective. – Treatment of a trialkenylborane with acetic acid results in stereoselective replacement of B by H. B RR H 3CH 3 CO H O HH (CH 3 COO) 3 B cis - 3-Hexene + A trialkenylborane + BH 3 THF B R R 3-Hexyne + A trialkenylborane (R = cis- 3-hexenyl group) H 3 Organic Lecture Series 6 Organic Synthesis Organic Synthesis • A successful synthesis must –provide the desired product in maximum yield. –have the maximum control of stereochemistry and regiochemistry. • The strategy will be to work backwards from the target molecule.
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Organic Lecture Series 7 • Analyze a target molecule in the following ways: – The carbon skeleton: how can we put it together? Our only method to date for forming a new C-C bond is the alkylation of alkyne anions. – The functional groups: what are they, how can they be used in forming the carbon-skeleton of the target molecule, and will they be changed by the reaction conditions to give the functional groups of the target molecule? Organic Synthesis Organic Synthesis Organic Lecture Series 8 • A method called a retrosynthesis is used and an open arrow symbolizes a step or series of steps in a retrosynthesis.
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This note was uploaded on 03/20/2011 for the course CHEMISTRY 310m taught by Professor Iverson during the Fall '08 term at University of Texas at Austin.

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lecture 16 (ch 7) - Organic Lecture Series CH 310/318 M...

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