162:
129:
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62:
in an electrocyclization appear to rotate over the course of the reaction, and thus selection of a single product is equivalent to selection of one direction of rotation (i.e. the direction of torque on the substituents). The concept was originally developed by
183:
Jefford, C.W.; Bernardinelli, G.; Wang, Y.; Spellmeyer, D.C.; Buda, A.; Houk, K.N. (1992), "Torquoselectivity in the
Electrocyclic Conversion of Benzocyclobutenes to o-Xylylenes",
105:
Conrotatory and disrotatory modes of rotation each showing two possible directions of rotation that result in pairs of enantiomers for a generic hexatriene system.
82:
of a cyclization product is formed from the selective ring closure of the starting material. In a typical electrocyclic ring closing, selection for either
109:
in the case shown, there is no reason for the reaction to be torquoselective and both products would be expected for any particular set of conditions.
121:
is often the driving force for the selectivity. Studies have shown that the selectivity can also be changed by the presence of electron donating and
113:
Torquoselectivity is also used to describe selective electrocyclic ring openings, in which different directions of rotation produce distinct
211:
Kirmse, W.; Rondan, N.G.; Houk, K.N. (1984), "Stereoselective
Substituent Effects on Conrotatory Electrocyclic Reactions of Cyclobutenes",
155:
154:), and axial-to-tetrahedral chirality transfer. An example of the latter case is shown below for the torquoselective
122:
165:
Torquoselectivity via axial to tetrahedral chirality transfer in the
Nazarov cyclization of allenyl vinyl ketones
273:
55:
43:
24:
241:
239:
Frontier, A. J.; Collison, C. (2005), "The
Nazarov cyclization in organic synthesis. Recent advances.",
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95:
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114:
75:
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Thermal electrocyclic ring opening of a cyclobutene giving selectivity via steric strain
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reactions modes still produces two enantiomers. Torquoselectivity is a discrimination
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Other mechanisms by which torquoselectivity can operate include
31:, defined as "the preference for inward or outward rotation of
54:, as it represents a further level of selectivity beyond the
46:." Torquoselectivity is not to be confused with the normal
150:(in which case the torquoselectivity is a case of
8:
58:. The name derives from the idea that the
94:these possible enantiomers that requires
175:
7:
158:of a chiral allenyl vinyl ketone.
14:
1:
156:Nazarov cyclization reaction
146:, induction via neighboring
123:electron withdrawing groups
290:
255:10.1016/j.tet.2005.05.019
44:electrocyclic reactions
25:electrocyclic reactions
166:
133:
110:
74:, it is an example of
72:ring closing reactions
56:Woodward-Hoffman rules
164:
131:
104:
19:is a special kind of
152:diastereoselectivity
96:asymmetric induction
52:pericyclic reactions
48:diastereoselectivity
227:10.1021/ja00337a067
199:10.1021/ja00030a005
78:, wherein a single
167:
134:
117:. In these cases,
115:structural isomers
111:
76:enantioselectivity
249:(32): 7577–7606,
221:(25): 7989–7991,
214:J. Am. Chem. Soc.
186:J. Am. Chem. Soc.
29:organic chemistry
21:stereoselectivity
17:Torquoselectivity
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193:(4): 1157–1165,
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274:Stereochemistry
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65:Kendall N. Houk
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148:stereocenters
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119:steric strain
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60:substituents
33:substituents
23:observed in
16:
15:
242:Tetrahedron
88:disrotatory
84:conrotatory
41:disrotatory
37:conrotatory
170:References
141:Lewis acid
80:enantiomer
144:catalysts
268:Category
50:seen in
92:between
138:chiral
107:Note:
70:For
251:doi
223:doi
219:106
195:doi
191:114
86:or
39:or
35:in
27:in
270::
247:61
245:,
217:,
189:,
125:.
98:.
67:.
253::
225::
197::
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