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Regioselective reductive openings of 4,6-benzylidene acetals: synthetic and mechanistic aspects.

Ohlin, Markus LU ; Johnsson, Richard LU and Ellervik, Ulf LU (2011) In Carbohydrate Research 346. p.1358-1370
Abstract
The use of benzylidene acetals as protecting groups in carbohydrate chemistry is utterly important. The main advantage of benzylidene acetal is the ability for regioselective openings. 4,6-benzylidene acetal can be opened selectively under reductive conditions to yield either free 4-OH or 6-OH. There are a plethora of methods available for regioselective openings, but only a few of these are widely used. In recent years, the mechanism has been investigated for borane mediated openings and it seems likely that the regioselectivity is determined by borane, rather than Lewis acid. When borane is activated by Lewis acids, borane is the most electrophilic species that consequently coordinates to the most nucleophilic oxygen of the acetals,... (More)
The use of benzylidene acetals as protecting groups in carbohydrate chemistry is utterly important. The main advantage of benzylidene acetal is the ability for regioselective openings. 4,6-benzylidene acetal can be opened selectively under reductive conditions to yield either free 4-OH or 6-OH. There are a plethora of methods available for regioselective openings, but only a few of these are widely used. In recent years, the mechanism has been investigated for borane mediated openings and it seems likely that the regioselectivity is determined by borane, rather than Lewis acid. When borane is activated by Lewis acids, borane is the most electrophilic species that consequently coordinates to the most nucleophilic oxygen of the acetals, usually O-6. This results in the formation of 6-O-benzyl ethers. If borane is not activated, Lewis acid is the most electrophilic species that thus adds to O-6 and hence generates the 4-O-benzyl ether. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Carbohydrate Research
volume
346
pages
1358 - 1370
publisher
Elsevier
external identifiers
  • wos:000292852100002
  • pmid:21531396
  • scopus:79959984073
ISSN
1873-426X
DOI
10.1016/j.carres.2011.03.032
language
English
LU publication?
yes
id
b0a5a1e0-a57c-4a05-97f6-10ee7df33e40 (old id 1973326)
date added to LUP
2011-06-21 17:48:19
date last changed
2017-05-21 03:19:57
@article{b0a5a1e0-a57c-4a05-97f6-10ee7df33e40,
  abstract     = {The use of benzylidene acetals as protecting groups in carbohydrate chemistry is utterly important. The main advantage of benzylidene acetal is the ability for regioselective openings. 4,6-benzylidene acetal can be opened selectively under reductive conditions to yield either free 4-OH or 6-OH. There are a plethora of methods available for regioselective openings, but only a few of these are widely used. In recent years, the mechanism has been investigated for borane mediated openings and it seems likely that the regioselectivity is determined by borane, rather than Lewis acid. When borane is activated by Lewis acids, borane is the most electrophilic species that consequently coordinates to the most nucleophilic oxygen of the acetals, usually O-6. This results in the formation of 6-O-benzyl ethers. If borane is not activated, Lewis acid is the most electrophilic species that thus adds to O-6 and hence generates the 4-O-benzyl ether.},
  author       = {Ohlin, Markus and Johnsson, Richard and Ellervik, Ulf},
  issn         = {1873-426X},
  language     = {eng},
  pages        = {1358--1370},
  publisher    = {Elsevier},
  series       = {Carbohydrate Research},
  title        = {Regioselective reductive openings of 4,6-benzylidene acetals: synthetic and mechanistic aspects.},
  url          = {http://dx.doi.org/10.1016/j.carres.2011.03.032},
  volume       = {346},
  year         = {2011},
}