NO3 induced self-terminating radical oxygenations: Diastereoselective synthesis of anellated pyrrolidines

Australian Journal of Chemistry

Volumn 57, Issue 11, 2004, Pages 1055-1066

  Stademann, Arne ^a   Wille, Ufa ^b  

^a UNIVERSITY OF KIEL   (Germany)

^b UNIVERSITY OF MELBOURNE   (Australia)

Author keywords

[No Author keywords available]

Indexed keywords

COLUMN CHROMATOGRAPHY; ETHERS; HYDROGEN; IRRADIATION; NITROGEN COMPOUNDS; OXIDATION; PHOTOCHEMICAL REACTIONS; REACTION KINETICS;

CYCLIZATION; PYRROLIDINES; RADICALS; STEREOELECTRONIC EFFECTS;

STEREOCHEMISTRY;

EID: 10644238098     PISSN: 00049425     EISSN: None     Source Type: Journal    
DOI: 10.1071/CH04124     Document Type: Article

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56. The concept of radical stability and stabilization is currently undergoing a complete re-evaluation; see for example: (a) M. L. Coote, A. Pross, L. Radom, Org. Lett. 2003, 5, 4689. doi:10.1021/OL035860+ (b) N. Malsunaga, D. W. Rogers, A. A. Zavitsas, J. Org. Chem. 2003, 68, 3158. doi:10.1021/JO020650G (c) A. A. Zavitsas, J. Chem. Ed. 2001, 78, 417. However, stabilization of a reaction centre by acceptor or donor substituents, commonly known as capto or dative effects, respectively, is a well accepted concept in chemistry. In the case of radicals, this stabilization is due to orbital interactions between the SOMO and the HOMO dative) or LUMO (capto), which result in a decrease of the overall energy of the system; see also the following reference. (d) T. Linker, M. Schmittel, Radikale und Radikalionen in der Organischen Synthese 1999 (Wiley-VCH: Weinheim) and ref. [31].
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58. The concept of radical stability and stabilization is currently undergoing a complete re-evaluation; see for example: (a) M. L. Coote, A. Pross, L. Radom, Org. Lett. 2003, 5, 4689. doi:10.1021/OL035860+ (b) N. Malsunaga, D. W. Rogers, A. A. Zavitsas, J. Org. Chem. 2003, 68, 3158. doi:10.1021/JO020650G (c) A. A. Zavitsas, J. Chem. Ed. 2001, 78, 417. However, stabilization of a reaction centre by acceptor or donor substituents, commonly known as capto or dative effects, respectively, is a well accepted concept in chemistry. In the case of radicals, this stabilization is due to orbital interactions between the SOMO and the HOMO dative) or LUMO (capto), which result in a decrease of the overall energy of the system; see also the following reference. (d) T. Linker, M. Schmittel, Radikale und Radikalionen in der Organischen Synthese 1999 (Wiley-VCH: Weinheim) and ref. [31].
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60. 3 induced, self-terminating radical oxygenations of 1 (X = O) have revealed that the orientation of the nitrate substituent relative to the 5-hexenyl chain has no influence on the diastereoselectivity of the 5-exo cyclization, when R is a non-polar substituent (i.e. methyl); ref. [7].
61. Formation of 23 could principally be also explained through a 1,3-HAT, followed by 3-ezo cyclization, according to 3→29→30. However, since a 1,3-HAT in radical chemistry is practically unknown (see ref. [31]), we believe that 23 is formed via two subsequent 1,5-HATs, followed by a 3-exo cyclization, as shown in Scheme 5.