ORGANIC
LETTERS
2
001
Vol. 3, No. 17
753-2756
Stereoselective Synthesis of
Z)-Enethiols and Their Derivatives:
Vinylic S 2 Reaction of
2
(
N
3
(E)-Alkenyl(phenyl)-λ -iodanes with
Thioamides
Masahito Ochiai,* Shinji Yamamoto, Takashi Suefuji, and Da-Wei Chen
Faculty of Pharmaceutical Sciences, UniVersity of Tokushima, 1-78 Shomachi,
Tokushima 770-8505, Japan
Received June 27, 2001
ABSTRACT
3
Exposure of (E)-â-alkylvinyl(phenyl)-λ -iodanes to thioamides in dichloromethane at room temperature was found to result in a bimolecular
N N
nucleophilic substitution (S 2) at the vinylic carbon atom to give inverted (Z)-enethiols and/or (Z)-S-vinylthioimidonium salts. Vinylic S 2
reactions with thioureas are also discussed.
3
Hypervalent alkenyl(phenyl)-λ -iodanes are highly reactive
mamides with rather low nucleophilicity also act as a
species in the reaction with nucleophiles because of the very
nucleophile toward (E)-â-alkylvinyliodanes 1 and afford (Z)-
vinyl formates stereoselectively via vinylic S
3
1
2 reaction.4
N
high leaving ability of λ -phenyliodanyl groups. We were
3
interested to see that (E)-â-alkylvinyl(phenyl)-λ -iodanes 1
This reaction requires heating at 50 °C. We report herein
3
underwent a bimolecular nucleophilic substitution (S
N
2) at
N
vinylic S 2 reaction of (E)-â-alkylvinyl(phenyl)-λ -iodanes
2
the vinylic carbon atoms, given that vinylic S
N
2 reactions
1 with thioamides, which proceeds under mild conditions
and yields (Z)-enethiols and/or (Z)-S-vinylthioimidonium
salts with exclusive inversion of configuration, depending
on the structure of thioamides and/or on the workup
procedure.
have been considered to be high-energy, low-probability
processes and, as such, have been neglected for a long time.
N
Nucleophiles that may participate in vinylic S 2 reaction with
1
include halides, dialkyl sulfides and selenides, phosphoro-
1
,3
selenoates, dithiocarbamates, and carboxylic acids. For-
Thioamides are more nucleophilic than the corresponding
5
3
amides, and thus nucleophilic substitutions of (E)-λ -
vinyliodanes 1 with thioamides proceed even at room
temperature. However, in contrast to the reaction with
formamides that affords inverted (Z)-vinyl formates stereo-
selectively, no formation of the corresponding (Z)-vinyl
thioformates was observed in the reaction with thioforma-
(1) (a) Ochiai, M. J. Organomet. Chem. 2000, 611, 494. (b) Ochiai, M.
In Chemistry in HyperValent Compounds; Akiba, K., Ed.; Wiley-VCH: New
York, 1999; Chapter 12. (c) Koser, G. F. In The Chemistry of Functional
Groups, Supplement D2; Patai, S., Rappoport, Z., Eds.; Wiley: New York,
1
995; Chapter 21.
2) (a) Ochiai, M.; Oshima, K.; Masaki, Y. J. Am. Chem. Soc. 1991,
13, 7059. (b) Okuyama, T.; Takino, T.; Sato, K.; Ochiai, M. J. Am. Chem.
(
1
Soc. 1998, 120, 2275. (c) Okuyama, T.; Takino, T.; Sato, K.; Oshima, K.;
Imamura, S.; Yamataka, H.; Asano, T.; Ochiai, M. Bull. Chem. Soc. Jpn.
(4) Ochiai, M.; Yamamoto, S.; Sato, K. J. Chem. Soc., Chem. Commun.
1999, 1363.
(5) Ohno, A. In Organic Chemistry of Sulfur; Oae, S., Ed.; Plenum
Press: New York, 1977; Chapter 5.
1
998, 71, 243.
3) (a) Yan, J.; Chen, Z.-C. Tetrahedron Lett. 1999, 40, 5757. (b) Yan,
J.; Chen, Z.-C. Synth. Commun. 1999, 29, 2867.
(
1
0.1021/ol016356c CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/26/2001