2444-092811

2444-092811 - 1 Specific Starting Material These fragments are pieces of a molecule(call them disconnect products sometimes they are called retrons

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Specific Starting Material 1 • These fragments are pieces of a molecule (call them disconnect products ; sometimes they are called retrons ). In order to determine the reaction required for the synthesis, convert the disconnect fragments into real molecules. • Focus on translating the fragments into real molecules. This process will allow an evaluation of both chemical reaction, in the context of this speci±c synthesis. • This translation of disconnect fragments to real molecules involves the use of a synthetic equivalent . OH 9 a b b a OH OH 10 11 13 disconnect disconnect 12
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Specific Starting Material 2 • A nucleophilic carbon is a donor carbon and an electrophilic carbon is an acceptor carbon. The carbon that was part of the disconnected bond, marked with a , may be either a donor or an acceptor. If that carbon is designated as a donor in 13 donor , then the analogous carbon in 12 acceptor must be an acceptor. Conversely, if that carbon in 13 acceptor is designated as an acceptor, then the analogous carbon in 12 donor must be a donor. • Examine both possibilities, but use the natural bond polarization as a guide . OH 12 donor 13 acceptor OH 12 acceptor 13 donor donor acceptor acceptor donor
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Specific Starting Material 3 The natural bond polarization of O-C is ! - O-C + and that carbon is naturally an electron acceptor. Attempts to make that carbon negative (a donor) is contrary to the normal bond polarization. • What structural feature is required to make the donor carbon of 13 dnor a real molecule? • Fragments 12 acceptor and 13 donor must be converted into a real molecule using the concept of a synthetic equivalent: a fragment that represents a real molecule . OH 12 donor 13 acceptor OH 12 acceptor 13 donor donor acceptor acceptor donor
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Disconnect Products and Synthetic Equivalents 4 OH 12 donor 13 acceptor OH 12 acceptor 13 donor donor acceptor acceptor donor C donor C O C donor RO C donor C O CH 2 N- C donor R-C= C donor R-C- C donor C acceptor C-X O= C acceptor O- C acceptor O=C O-C- C acceptor C C O C-MgX , X-Li N ! C donor N ! C R-C ! C donor R-C ! C Disconnect Fragment Synthetic Equivalent
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Disconnect Products and Synthetic Equivalents 5 OH 12 donor 13 acceptor OH 12 acceptor 13 donor donor acceptor acceptor donor OH 12 acceptor 13 donor acceptor donor O MgBr 15 14 acceptor donor
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Disconnect Products and Synthetic Equivalents 6 OH 12 acceptor 13 donor acceptor donor O MgBr 15 14 acceptor donor Now disconnect the ketone to take one more step back to the starting material. O 15 b c O O 10 16 17 18 b disconnect disconnect O MgBr O H 10 donor donor acceptor 16 acceptor 19 20 Based on: O H MgBr OH H 19 20 21 1. ether 2. H 3 O + +
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Functional Group Manipulation 7 • A synthesis cannot succeed unless the chemical relationship between those functional groups is recognized.
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This note was uploaded on 02/25/2012 for the course CHEM 244 taught by Professor Jardin,j during the Fall '08 term at UConn.

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2444-092811 - 1 Specific Starting Material These fragments are pieces of a molecule(call them disconnect products sometimes they are called retrons

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