BULLETIN OF THE
Communication
KOREAN CHEMICAL SOCIETY
treatment of 1i with 30 mol% of B(C6F5)3 was effective to
form 4a as a single isomer (Method B). Under the same
conditions, dimethyl-substituted arene 1j was also
converted to 4b with comparable results. It is noteworthy
mentioning that cis vinyloxiranes 1k and 1l were cyclized
to 5a and 5b, respectively, without scrambling stereochem-
istry under the same conditions as trans vinyloxiranes
(Scheme 3).
To demonstrate the potential use of resulting cyclic com-
pounds as key intermediates in the synthesis of musellarins,
we carried out each diastereomers 2a and 3a to form the
corresponding acrylic ester. Then, ring-closing metathesis
of the esters afforded the γ-lactones with the requisite cis-
and trans stereochemistry for the construction of musellarin
A and E (Scheme 4).11
Scheme 3. Extension to seven-membered ring system.
In conclusion, we described efficient catalytic system for
regio- and stereoselective carbocyclizations of cis- and
trans-vinyloxiranes. The carbocyclization delivered six-
and seven-membered rings with a wide range of substrate
scope. The synthetic utility of this method was demon-
strated in the concise synthesis of the tricyclic core of
musellarins. Further investigations for asymmetric method
and syntheses of musellarin A and E are in progress.
Acknowledgments. This research was funded by the
National Research Foundation of Korea (NRF-
2018R1D1A1B07044008).
Supporting Information. Additional supporting informa-
tion may be found online in the Supporting Information
section at the end of the article.
Scheme 4. Construction of the musellarin skeleton.
of cis 3a (85:15–80:20 dr, Table 1, entries 3 and 4). Fortu-
nately, we were delighted to find that unique catalyst
B(C6F5)3 can be efficiently catalyzed the stereoselective
cyclization in CH2Cl2 at −78 C affording cis 3a as a sin-
gle isomer (Table 1, entry 7).
References
1. For general discussions, see reviews(a)B. Olofsson, P.
Somfai, Aziridines and Epoxides in Organic Synthesis, A. K.
Yudin Ed., Wiley-VCH, Weinheim, Germany, 2006, p. 315.
(b) J. He, J. Ling, P. Chiu, Chem. Rev. 2014, 114, 8037.
2. (a) E. S. Huyser, L. R. Munson, J. Org. Chem. 1965, 30,
1436. (b) N. Charrier, D. Gravestock, S. Zard, Angew. Chem.
Int. Ed. 2006, 45, 6520. (c) S. Kim, S. Lee, J. S. Koh, J. Am.
Chem. Soc. 1991, 113, 5106. (d) Y. Ogawa, K. Kuroda, T.
Mukaiyama, Chem. Lett. 2005, 34, 698.
3. (a) A. Decortes, M. M. Belmonte, J. Benet-Buchholz, A. W.
Kleij, Chem. Commun. 2010, 46, 4580. (b) A. Coletti, C. J.
Whiteoak, V. Conte, A. W. Kleij, ChemCatChem 2012,
4, 1190.
4. (a) S. K. Taylor, D. L. Clark, K. L. Heinz, S. B. Schramm,
C. D. Westermann, K. K. Barnell, J. Org. Chem. 1983, 48,
592. (b) S. Nagumo, I. Miyoshi, H. Akita, N. Kawahara, Tet-
rahedron Lett. 2002, 43, 2223.
5. (a) J. Lee, S.-G. Kim, Bull. Kor. Chem. Soc. 2019, 40, 606.
(b) K. J. Lee, G. Kim, Bull. Kor. Chem. Soc 2018, 39, 1239.
Also please see reviews(c)B. Maji, Adv. Synth. Catal 2019,
361, 3453. (d) T. Nemoto, Y. Hamada, Synlett 2016,
27, 2301.
ꢀ
With these observations in hand, cis- and trans substrates
varying substitutions of arenes were evaluated to establish
optimal conditions. Based on the preliminary results, cycli-
zations of trans vinyloxiranes in the presence of 50 mol %
ꢀ
BF3ÁOEt2 at −78 C for 2 h (Table 2, entries 1–4, Method
A) led to high levels of diastereoselectivity in all cases.
In addition, B(C6F5)3 was successfully employed to the
cis substrates for the transformations providing cis adducts
3 in good yields with excellent stereoselectivity regardless
of electronic effect from the substituents of arenes (Table 2,
entries 5–8, Method B).
This result prompted us to explore an extension to
seven-membered ring system. According to the conditions
for trans vinyloxiranes, we first examined trans 1i with
50 mol % of BF3ÁOEt2 (Method A), but isolated 4a in only
marginal results. Although cyclized product 4a was pro-
duced during the reaction, problems of low yield (30%)
and formation of several unidentified side products
remained to be solved. Gratifyingly, we found that
6. D. S. Jang, E. J. Park, M. E. Hawthorne, J. S. Vigo, J. G.
Graham, F. Cabieses, B. D. Santarsiero, A. D. Mesecar,
Bull. Korean Chem. Soc. 2021, Vol. 42, 667–670
© 2021 Korean Chemical Society, Seoul & Wiley-VCH GmbH
669