Tin-free generation of alkyl radicals from alkyl 4-pentynyl sulfides via homolytic substitution at the sulfur atom

Organic Letters

Volumn 10, Issue 6, 2008, Pages 1127-1130

  Bencivenni, Giorgio ^a   Lanza, Tommaso ^a   Leardini, Rino ^a   Minozzi, Matteo ^a   Nanni, Daniele ^a   Spagnolo, Piero ^a   Zanardi, Giuseppe ^a  

^a UNIVERSITY OF BOLOGNA   (Italy)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 56249121594     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol800046k     Document Type: Article

References (18)

1. (a) Benati, L.; Calestani, G.; Leardini, R.; Minozzi, M.; Nanni, D.; Spagnolo, P.; Strazzari, S. Org. Lett. 2003, 5, 1313.
2. (b) Benati, L.; Leardini, R.; Minozzi, M.; Nanni, D.; Scialpi, R.; Spagnolo, P.; Zanardi, G. Synlett 2004, 987. For a nice review on homolytic substitution at the sulfur atom as a tool for organic synthesis,
3. see: (c) Crich, D. Helv. Chim. Acta 2006, 89, 2167. For comprehensive reviews on tin-free methodologies,
4. see: (d) Baguley, P. A.; Walton, J. C. Angew. Chem., Int. Ed. 1998, 37, 3072.
5. (e) Studer, A.; Amrein, S. Synthesis 2002, 835.
6. Benati, L.; Bencivenni, G.; Leardini, R.; Minozzi, M.; Nanni, D.; Scialpi, R.; Spagnolo, P.; Zanardi, G. J. Org. Chem. 2006, 71, 3192.
7. Carta, P.; Puljic, N.; Robert, C.; Dhimane, A.-L.; Fensterbank, L.; Lacôte, E.; Malacria, M. Org. Lett. 2007, 9, 1061.
8. Ooi, T.; Furuya, M.; Sakai, D.; Maruoka, K. Adv. Synth. Catal. 2001, 343, 166.
9. The whole synthetic array of possibilities was fully examined with sulfide 1f (see Supporting Information).
10. This is an improved procedure with respect to that previously reported (ref 1a), which started from 4-pentyn-1-ol. See also: Minozzi, M.; Nanni, D.; Spagnolo, P. 4-Pentyne-1-thiol. In The Encyclopedia of Reagents for Organic Synthesis (eEROS); Wiley: Chichester, 2008; Build 13, in press.
11. For general methods for conversion of thiolesters into thiols, see: Zheng, T.-C.; Burkart, M.; Richardson, D. E. Tetrahedron Lett. 1999, 40, 603 and references therein.
12. Azobis(cyclohexanecarbonitrile).
13. Mixtures of E- and Z-isomers. Under certain conditions and with some substrates an isomeric form of 3 was also isolated; studies are underway to determine its structure.
14. Hi mechanism at the sulfur atom is substantiated by the fact that unstabilized alkyl radicals can even be obtained by direct, one-pot treatment of the corresponding 4-pentynyl sulfides with benzenethiol, i.e., without syringe pump addition of the latter, although under these conditions significant amounts of vinyl sulfides 5 were also obtained.
15. 17). The corresponding pentynyl sulfides can be easily synthesised but cannot be purified, due to their instability under all types of workup. Some reactions carried out on the crude sulfides yielded the expected reduction products accompanied by unreacted starting material and other unidentified side products.
16. (a) Benati, L.; Leardini, R.; Minozzi, M.; Nanni, D.; Scialpi, R.; Spagnolo, P.; Strazzari, S.; Zanardi, G. Angew. Chem., Int. Ed. 2004, 43, 3598.
17. (b) Wan, Q.; Danishefsky, S. J. Angew. Chem., Int. Ed. 2007, 46, 9248, and references therein.
18. Cyclizations were carried out by adding the toluene solution of benzenethiol and ACCN in 4 h instead of the 2 h required for defunctionalizations.