Organic Letters
Letter
a
elemental sulfur to afford 1,2-thiaselenole-3-thione (4a) rather
than the desired product (4a′). This unprecedented rearrange-
ment may be driven by the thermodynamic instability of the
CSe bond in heterocycle 4a′. The similar rearrangement
happened to other cyclopropyleneselenones and afforded
corresponding products (4b−4g) in acceptable yields.
Scheme 4. Scope of Reaction Using Elemental Selenium
In the course of our study on the substrate scope, we found
that, in addition to the desired product 2o, a 22% yield of 2,5-
diphenyl-7λ4-[1,2]dithiolo[5,1-e][1,2]dithiole (5a)19 was iso-
lated in the reaction of 2-phenylcycloprop-2-en-1-one with
elemental sulfur (Scheme S3a, see the Supporting Informa-
tion). The control experiments demonstrated that this
transformation involved a spironolactone intermediate
for the generation of spironolactone from cyclopropenones,18
the reaction delivered an increased yield of 5a (Scheme 3).
Scheme 3. Substrate Scope of the Synthesis of
Thiathiopthene
Other monosubstituted cyclopropenones were also converted
into corresponding products (5b−5d) in acceptable yields,
while disubstituted cyclopropenones failed to afford the
desired products (5e and 5f) probably due to the steric effect.
As the construction of organic selenium compounds
attracted growing attention recently,20 we next tried to explore
the possibility of [3 + 2] cycloaddition between cyclo-
propenone derivatives and elemental selenium (Scheme 4).
After a systematical examination for additives, temperature,
solvent, and atmosphere, the transformation was found to be
facile in DMSO at 120 °C for 12 h. 4,5-Diaryl-3H-1,2-
diselenol-3-ones (6a−6e) were formed in 68%−85% yields by
treatment of symmetric cyclopropenones with elemental
selenium. Unfortunately, no formation of the desired products
(6f and 6g) was observed using unsymmetrical cyclo-
propenone as a substrate. Symmetrical diaryl cyclopropylene-
thiones worked well in this protocol and afforded correspond-
ing products (7a−7d) with moderate yields. The reaction of
unsymmetrical cyclopropylenethione with elemental selenium
gave a mixture (7e and 7e′) with a ratio of 6:1. It is
noteworthy that the resulting products 7a−7e were a new class
of heterocyclic compound. The formation of the desired
product (7f) was not observed using diethyl cyclopropylene-
thione. Interestingly, the reaction of diphenylcyclopropylene-
selenone yielded the hydrolysis product 6a rather than the
desired product 8a.
a
Reaction conditions: 1 (0.2 mmol), Se powder (0.4 mmol), DMSO
b
(2.0 mL), N2, 120 °C, 12 h, isolated yields. Conducted on 10 mmol.
c
A mixture with a ratio of 6:1.
products 2a and 6a (Scheme 5). 2a could be oxidized to
compound 8a in 60% yield while 6a failed to provide
compound 8b in the presence of m-CPBA. In addition, 6a
successfully underwent ring-opening/nucleophilic substitution
with alkyl iodides to furnish compounds 8c and 8d in
moderate yields.
As Table 1 showed, the employment of air or O2 atmosphere
led to a higher yield than the N2 atmosphere, implying that the
presence of O2 could promote this transformation. Inspired by
these results, we intended to examine the effect of other
oxidants or additives on reaction efficiency (Figure 1). The
addition of oxidants such as BQ, m-CPBA, and BuOOtBu
t
significantly accelerated the formation rate of product 2a, yet
completely inhibited the generation of product 6a. The low
yield of product 6a may result from easy oxidation of Se
powder at high temperature by these oxidants. Anecdotally, the
reactions gave improved yields of products 2a and 6a in the
presence of phenol, BHT, or 4-methoxyphenol. The formation
of product 4a was inhibited upon the addition of BQ while the
The synthetic utilization of this protocol has been
demonstrated by the postfunctionalization of the synthesized
C
Org. Lett. XXXX, XXX, XXX−XXX