Two-step allylic carbon insertion between ketone carbonyl and α carbons giving α-quaternary α-vinyl ketones

Article abstract of DOI:10.1016/j.tetlet.2008.09.068

Ketones 1 were converted to α-quaternary α-vinyl ketones 2 by a two-step formal allylic carbon insertion between ketone carbonyl and α carbons, which involves the reaction of 1 with propargyltitanium reagents, derived from propargyl carbonates 3 and a divalent titanium reagent Ti(O-i-Pr)₄/2i-PrMgCl, and the following rearrangement of the resulting α-allenyl alcohols 4 with NBS.

Full text of DOI:10.1016/j.tetlet.2008.09.068

Tetrahedron Letters 49 (2008) 6724–6727
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Two-step allylic carbon insertion between ketone carbonyl
and
a
carbons giving
a-quaternary
a-vinyl ketones
*
Jing-Qian He, Daisuke Shibata, Chihaya Ohno, Sentaro Okamoto
Department of Material and Life Chemistry, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Ketones 1 were converted to
between ketone carbonyl and
a
-quaternary
carbons, which involves the reaction of 1 with propargyltitanium
reagents, derived from propargyl carbonates 3 and a divalent titanium reagent Ti(O-i-Pr)4/2i-PrMgCl,
and the following rearrangement of the resulting -allenyl alcohols 4 with NBS.
Ó 2008 Elsevier Ltd. All rights reserved.
a-vinyl ketones 2 by a two-step formal allylic carbon insertion
Received 25 August 2008
Revised 9 September 2008
Accepted 12 September 2008
Available online 17 September 2008
a
a
Insertion of a carbon atom into a carbon–carbon bond is of
interest as a versatile synthetic means for chain elongations at an
internal position or ring expansions of cyclic compounds, thereby
allowing for unique transformations of the molecular framework,
but it is relatively difficult compared to chain extensions at the
terminal positions.1 Efforts have been devoted to realize such
transformation and many methylene insertion reactions (homolo-
gation) and related reactions have been developed, which involve
a
-diazo insertions,2 reactions with b-oxido carbenoids,3 (semi)-
pinacol-type rearrangements,4 ring expansions through radical
processes5 and other reactions.6 Herein disclosed is a formal two-
step allylic carbon insertion reaction between ketone carbonyl
Scheme 2. Plan for two-step conversion of ketones 1–2 by allenylation and
rearrangement (Z: leaving group).
and
a carbons, providing a-vinyl ketones with an a-quaternary
carbon (Scheme 1).
The present two-step reaction is outlined in Scheme 2, which
involves a selective allenyl addition reaction to cyclic and acyclic
ketones 1 followed by a rearrangement reaction of the resulting
Ma and co-workers.8 In addition, Pd-catalyzed rearrangement/ring
expansion reaction of 1-(1,2-dienyl)cyclobutanols (1-allenylcyclo-
butanols) have been reported,9 where the allenyl
p-coordinated
tertiary
a
-allenyl alcohols 4 with electrophilic reagents (X+). The
Pd was proposed as an initial intermediate. In order to selectively
allenylate the ketones, we used allenyl/propargyl titanium re-
agents derived from propargyl compounds 3 (Z = leaving group)
and a divalent titanium reagent, Ti(O-i-Pr)4/2i-PrMgCl.10 Readily
available propargyl alcohol derivatives 3 can be used as the alleny-
p
-donative nature of the allenyl moiety7 in 4 is desirable for the
generation of a carbocation intermediate in the pinacol-type rear-
rangement of 4 to 2, as exemplified by the related rearrangement
of acyclic secondary
a-allenyl alcohols with electrophilic reagents
to -vinyl aldehydes having an
a
a-quaternary carbon developed by
lating agent and can give nearly complete selectivity of
a-allenyl
alcohols with high yields.11
According to the reaction sequence shown in Scheme 2, we car-
ried out this two-step reaction on a variety of cyclic ketones 1 with
propargyl substrates 3 and N-bromosuccinimide (NBS) as an elec-
trophilic reagent. The results are summarized in Table 1, where the
crude mixture of an allenyl alcohol 4 derived from 1 and 3 was
used directly for the next rearrangement reaction and, therefore,
the yields listed are the overall yields of these two steps. The 1H
NMR analysis of the crude 4 showed exclusive formation of an alle-
nyl alcohol 4, where the corresponding homopropargylic alcohol
was not detected. In all cases, this two-step reaction provided
Scheme 1. Conceptual scheme of allylic carbon insertion to ketones.
* Corresponding author. Tel.: +81 45 481 5661; fax: +81 45 413 9770.
E-mail address: okamos10@kanagawa-u.ac.jp (S. Okamoto).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.09.068

J.-Q. He et al. / Tetrahedron Letters 49 (2008) 6724–6727
6725
Table 1
Table 2
Ring expansion reaction of cyclic ketonesa
Quaternary carbon insertion to acyclic ketonesa
3b
Product 2
Yieldc
Run
1
3b Product 2
Yieldc
Run
1
1
2
1g (R0 = Ph,
3b
3b
2hb (X = H): 70%
1
2
3
3a (R = Me)
3b (R = n-Bu)
3c (R = Ph)
2aa: R = Me, 38%
2ab: R = n-Bu, 66%
2ac: R = Ph, 59%
R00 = Me)
1h (R0 =
MeOC6H4, R00 = Me)
q
-
2gb (X = OMe): 85%
4
3b
2bb
79% (58%)d
(23%)e (trace)f
3
1i (R0 =
q-NC-C6H4, 3b
R00 = Me) 1i
5
6
7
8
3b
3b
3b
3b
2cb: 40%
2db: 70%
2eb: 57%
2fb: 47%
4
5
1j (R0 = R00 = n-Bu)
3c
2jc: 31%
1k (R0 = ꢁC„CPh,
R00 = n-Pr)
3b
2kb: 50%
6d
3b
2lb: 25%e
a
CH3CN:H2O = 15:1 (v/v).
For runs 1–6, 1.3 equiv of 1 and 1.0 equiv of 3 were used. For runs 7 and 8,
b
a
CH3CN:H2O = 15:1 (v/v).
For run 5, 1.3 equiv of 1 and 1.0 equiv of 3 were used. For runs 1–4 and 6,
1.0 equiv of 1 and 1.3 equiv of 3 were used.
b
c
Isolated yield.
The reaction with NBS in dry CH3CN.
The reaction with NBS in dry CH2Cl2.
The reaction with NBS in DMF.
1.0 equiv of 1 and 1.3 equiv of 3 were used.
d
c
Isolated yield.
1.0 equiv of 1l and 2.6 equiv of 3 were used.
2.6 equiv of NBS was used.
e
d
f
e
the corresponding rearrangement (ring expansion) product in
moderate to good yield.
9-BBN, THF then K3PO4, 5 mol % of Cl2Pd(dppf), THF, 70 °C) of
2ab proceeded smoothly with alkyne and organoborane counter-
parts to yield the corresponding products 6 and 7, respectively,
in high yields (Fig. 1) [dppf: 1,10-bis(diphenylphosphino)ferro-
cene]. Treatment of 2ab with n-BuZnI in the presence of
Cl2Pd(dppf) catalyst reduced alkenyl bromide to afford 8 having a
The results of a rearrangement reaction in several different
solvent(s), shown in run 4 of Table 1, revealed that the reaction
proceeded in CH3CN or CH2Cl2. Among them, wet CH3CN
(CH3CN:H2O = ꢀ15:1, v/v) gave better results, similar to the results
reported for the rearrangement of acyclic secondary allenyl alco-
hols by Ma and co-workers.8 As a substituent R in the substrate
propargyl carbonates, aliphatic and aromatic groups could be uti-
lized (runs 1–3). The rearrangement reaction of the allenyl alcohols
derived from unsymmetrical ketones 1d–f proceeded regioselec-
tively with cleavage of the sp2-carbon-carbonyl carbon bond to
provide the corresponding non-conjugated ketones 2db, 2eb and
2fb, respectively (runs 6–8).
The molecules obtained by the present two-step process shown
in Tables 1 and 2 have keto and vinyl bromide moieties useful for
further transformation.8 For example, Pd-catalyzed Sonogashira12
coupling (phenylacetylene, 5 mol % of Cl2Pd(PPh3)2, 15 mol % of
CuI, piperidine, THF, rt) and Suzuki–Miyaura13 coupling (styrene,
vinyl group at the a-position.
Next, we discuss on an extension of the present two-step trans-
formation to reactions with acyclic ketones. The results are shown
in Table 2, where the yields listed are the overall yields of these
two steps. In all cases, the allenylation of the ketones was nearly
quantitative and had exclusive regioselectivity. Ma and co-workers
have shown an example of
a-quaternary ketone formation from
acyclic tertiary 2,3-allenol 4 (R = Et, R0 = Ph, R00 = Me), derived from
acetophenone by In-mediated allenylation with 1-bromo-2-pen-
tyne (30% yield), giving the corresponding 2 in 83% yield by the
reaction with Br2.8b Similarly, the reaction of
a
-allenyl alcohols
4hb and 4gb, prepared from acetophenone (1g) and its derivatives

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J.-Q. He et al. / Tetrahedron Letters 49 (2008) 6724–6727
References and notes
1. (a) Wovkulich, P. M. In Comprehensive Organic Synthesis; Trost, B. M., Ed.;
Springer: Berlin, 1991; Vol. 1, p 843; (b) Hesse, M. Ring Enlargement in Organic
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2. (a) Maruoka, K.; Concepcion, A. B.; Yamamoto, H. J. Org. Chem. 1994, 59, 4725;
(b) Maruoka, K.; Concepcion, A. B.; Yamamoto, H. Synthesis 1994, 1283; (c)
Padwa, A.; Hornbuckle, S. F.; Zhang, Z.; Zhi, L. J. Org. Chem. 1990, 55, 5297; (d)
Holmquist, C. R.; Roskamp, E. J. J. Org. Chem. 1989, 54, 3258; (e) Nagao, K.;
Chiba, M.; Kim, S.-W. Synthesis 1983, 197; (f) Loeschorn, C. A.; Nakajima, M.;
McCloskey, P. J.; Anselme, J.-P. J. Org. Chem. 1983, 48, 4407; (g) Mock, W. L.;
Hartman, M. E. J. Org. Chem. 1977, 42, 459; (h) Gutsche, C. D.; Johnson, H. E. J.
Am. Chem. Soc. 1955, 77, 109.
Figure 1. Derivatization products from 2ab.
3. (a) Satoh, T.; Mizu, Y.; Kawashima, T.; Yamakawa, K. Tetrahedron 1995, 51, 703;
(b) Satoh, T.; Itoh, N.; Gengyo, K.; Yamakawa, K. Tetrahedron Lett. 1992, 33,
7543; (c) Satoh, T.; Hayashi, Y.; Mizu, Y.; Yamakawa, K. Tetrahedron Lett. 1992,
33, 7181; (d) Satoh, T.; Fujii, T.; Yamakawa, K. Bull. Chem. Soc. Jpn. 1990, 63,
1266; (e) Villieras, J.; Perriot, P.; Normant, J. F. Synthesis 1979, 968; Taguchi, H.;
Yamamoto, H.; Nozaki, H. Tetrahedron Lett. 1976, 2617; (f) Taguchi, H.;
Yamamoto, H.; Nozaki, H. J. Am. Chem. Soc. 1974, 96, 6510.
4. (a) Katritzky, A. R.; Toader, D.; Xie, L. J. Org. Chem. 1996, 61, 7571; (b) Krief, A.;
Dumont, W.; Laboureur, J. L. Tetrahedron Lett. 1988, 29, 3265; (c) Gadwood, R.
C.; Mallick, I. M.; DeWinter, A. J. J. Org. Chem. 1987, 52, 774; (d) Laboureur, J. L.;
Krief, A. Tetrahedron Lett. 1984, 25, 2713; (e) Gadwood, R. C. J. Org. Chem. 1983,
48, 2098; (f) Labar, D.; Laboureur, J. L.; Krief, A. Tetrahedron Lett. 1982, 23, 983;
(g) Sisti, A. J.; Rusch, G. M.; Sukhon, H. K. J. Org. Chem. 1971, 36, 2030; (h) Sisti,
A. J. Tetrahedron Lett. 1967, 5327; (i) Sisti, A. J. J. Org. Chem. 1970, 35, 2670.
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J. J. Org. Chem. 1990, 55, 5442; (c) Dowd, P.; Choi, S.-C. J. Am. Chem. Soc. 1987,
109, 3493.
6. Katritzky, A. R.; Xie, L.; Toader, D.; Serdyuk, L. J. Am. Chem. Soc. 1995, 117,
12015.
7. (a) Modern Allene Chemistry; Krause, N., Hashmi, A. S. K., Eds.; Wiley-VHC:
Weinheim, 2004; (b) Zimmer, R.; Dinesh, C. U.; Nandanan, E.; Khan, F. A. Chem.
Rev. 2000, 100, 3067.
Scheme 3. Proposed reaction mechanism.
1 h by the reaction with 3b and a divalent titanium, with NBS pro-
ceeded with a 1,2-shift of the aryl moiety to produce the corre-
sponding non-conjugated ketones 2hb and 2bg in 70% and 85%
overall yields, respectively (runs 1–2). However, the reaction start-
ing from 1i having an electron-withdrawing group (CN) at the 4
position yielded an equal amount of the rearrangement product
8. (a) Fu, C.; Li, J.; Ma, S. Chem. Commun. 2005, 4119; (b) Li, J.; Fu, C.; Chen, G.;
Chai, G.; Ma, S. Adv. Synth. Catal. 2008, 350, 1376.
2ib and the epoxide 5 (run 3). Alkyl group migration in the a-alle-
9. Pd-
, Rh- or Ru-catalyzed ring expansion reactions of allenylcyclobutanol
derivatives: (a) Trost, B. M.; Xie, J. J. Am. Chem. Soc. 2008, 130, 6231; (b)
Wender, P. A.; Deschamps, N. M.; Sun, R. Angew. Chem., Int. Ed. 2006, 45, 3957;
(c) Trost, B. M.; Xie, J. J. Am. Chem. Soc. 2006, 128, 6044; (d) Yoshida, M.;
Sugimoto, K.; Ihara, M. Tetrahedron 2002, 58, 7839; (e) Yoshida, M.; Sugimoto,
K.; Ihara, M. Tetrahedron Lett. 2001, 42, 3877; (f) Yoshida, M.; Sugimoto, K.;
Ihara, M. Tetrahedron Lett. 2000, 41, 5089; (g) Nemoto, H.; Yoshida, M.;
Fukumoto, K. J. Org. Chem. 1997, 62, 6450. See also,; (h) Yoshida, M.;
Komatsuzaki, Y.; Nemoto, H.; Ihara, M. Org. Biomol. Chem. 2004, 2, 3099.
10. (a) Sato, F.; Urabe, H.; Okamoto, S. Chem. Rev. 2000, 100, 2835; (b) Kulinkovich,
O. G.; de Meijere, A. Chem. Rev. 2000, 100, 2789; (c) Eisch, J. J. J. Organomet.
Chem. 2001, 617–618, 148–157; (d) Sato, F.; Okamoto, S. Adv. Synth. Catal. 2001,
343, 759; (e) Sato, F.; Urabe, H. In Titanium and Zirconium in Organic Synthesis;
Marek, I., Ed.; Wiley-VCH: Weinheim, Germany, 2002; pp 319–354.
11. (a) Nakagawa, T.; Kasatkin, A.; Sato, F. Tetrahedron Lett. 1995, 36, 3207; (b)
Okamoto, S.; Sato, H.; Sato, F. Tetrahedron Lett. 1996, 37, 8865; (c) Delas, C.;
Okamoto, S.; Sato, F. Tetrahedron Lett. 2002, 43, 4373. See also, Ref. 2a and (d)
Yamamoto, H. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.;
Pergamon Press: Oxford, 1991; p 81. Vol. 2.
12. (a) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975, 4467; (b)
Sonogashira, K. J. Organomet. Chem. 2002, 653, 46.
13. Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
14. Typical procedure: To a mixture of 3b (1.0 mmol) and Ti(O-i-Pr)4 (1.3 mmol) in
ether (10 mL) was added i-PrMgCl (2.6 mmol, 1.3 M in ether, 2.0 mL) at ꢁ40 °C.
After being stirred for 1.5 h at this temperature, cyclohexanone (1b)
(1.3 mmol) was added and then the mixture was gradually warmed to room
temperature over 2 h. After addition of saturated aqueous NaHCO3 (0.3 mL),
NaF (1 g) and Celite (1 g), the mixture was filtered through a pad of Celite with
ether. The filtrate was concentrated in vacuo to give a crude residue, which was
directly used for the next reaction. To a solution of the residue in CH3CN/H2O
(ꢀ15:1, v/v, 6 mL) was added portionwise NBS (1.3 mmol) at ambient
temperature. After being stirred for 2–4 h, saturated aqueous NaHCO3
(10 mL) was added. The mixture was extracted with ether, dried over MgSO4
and concentrated in vacuo. The resulting residue was subjected to column
chromatography on silica gel to afford 2bb (0.79 mmol) in 79% yield.
nyl alcohol derived from aliphatic ketone 1j was possible to pro-
duce the corresponding rearrangement product 2jc, albeit low
yield (run 4). Treatment of the allenyl intermediate derived from
ynone 1k with NBS rearranged an alkynyl group selectively (run
5). As exemplified in run 6, a tandem reaction starting from dike-
tone such as 1l was possible, although the reaction was not
optimized.
As illustrated in Scheme 3, it may be proposed that the rear-
rangement reaction proceeds through a carbocation intermediate
i generated by the reaction of allenyl alcohol 4 with NBS. When
an unsymmetrical ketone was utilized as a starting material, the
carbon migration from i occurred predominantly with an sp2 or
sp carbon (path a) to provide non-conjugated ketone product 2
selectively. This trend is similar to that observed in other cationic
1,2-migrations that proceed by pinacol-type rearrangement.1,4
When a rearrangement is slow, i competitively undergoes epoxide
formation (path c) as seen in the reaction of 1i (run 3 in Table 2).
In summary, we have demonstrated that the two-step reaction
involving a highly regioselective allenylation of ketones by utiliz-
ing allenyl/propargyl-titanium reagents, derived from propargyl
carbonates and a Ti(O-i-Pr)4/2i-PrMgCl reagent, followed by rear-
rangement by treatment with NBS of the resulting tertiary a-alle-
nyl alcohols provides a facile means for ring-expansion or one-
carbon elongation of ketones by a formal allylic carbon insertion
between carbonyl and
was not necessarily high, the method might be synthetically useful
a
carbons.14,15 Although the yield obtained
15. 1H NMR data of 2 (500 MHz, CDCl3) d: Compound 2aa; 5.71 (d, J = 2.5 Hz, 1H),
5.66 (d, J = 2.5 Hz, 1H), 2.62–2.71 (m, 1H), 2.34–2.45 (m, 2H), 1.99–2.08 (m,
1H), 1.42–1.90 (m, 4H), 1.25 (s, 3H). Compound 2ab; 5.81 (d, J = 2.0 Hz, 1H),
5.70 (d, J = 2.0 Hz, 1H), 2.65 (dt, J = 5.5, 13.0 Hz, 1H), 2.31–2.42 (m, 2H), 1.99–
2.07 (m, 1H), 1.05–1.91 (m, 10H), 0.90 (t, J = 7.3 Hz, 3H). Compound 2ac; 7.25–
7.42 (m, 5H), 5.74 (d, J = 2.5 Hz, 1H), 5.18 (d, J = 2.5 Hz, 1H), 2.70 (ddd, J = 4.0,
11.0, 14.5 Hz, 1H), 2.51–2.59 (m, 2H), 2.40 (dt, J = 15.0, 8.0 Hz, 1H), 1.70–1.92
(m, 4H). Compound 2bb; 5.74 (d, J = 2.3 Hz, 1H), 5.70 (d, J = 2.3 Hz, 1H), 2.72 (dt,
J = 2.9, 11.5 Hz, 1H), 2.38 (ddd, J = 2.9, 6.9, 11.5 Hz, 1H), 1.87–1.96 (m, 3H),
1.07–1.96 (m, 11H), 0.90 (t, J = 7.5 Hz, 3H). Compound 2cb; 5.88 (d, J = 2.0 Hz,
1H), 5.81 (d, J = 2.0 Hz, 1H), 2.96–3.03 (m, 1H), 2.14 (dt, J = 14.9, 4.6 Hz, 1H),
0.97–2.05 (m, 18H), 0.91 (t, J = 7.0 Hz, 3H). Compound 2db; 6.01 (d, J = 2.0 Hz,
1H), 5.97–6.03 (m, 1H), 5.79 (d, J = 2.0 Hz, 1H), 5.53 (dt, J = 12.0, 1.8 Hz, 1H),
because of the production of highly functionalized
a-quaternary
ketones which are otherwise difficult to prepare.16 In addition,
optimization of the reaction conditions for an individual substrate
may improve the yield. Application of the method to synthesis of
biologically active compounds is underway.
Acknowledgement
This study was partially supported by the Ministry of Education,
Culture, Sports, Science and Technology, Japan.

J.-Q. He et al. / Tetrahedron Letters 49 (2008) 6724–6727
6727
3.08 (ddd, J = 5.2, 8.1, 14.4 Hz, 1H), 2.49 (dt, J = 4.6, 9.2 Hz, 1H), 2.27–2.37 (m,
1H), 2.06–2.17 (m, 2H), 1.88 (ddd, J = 5.7, 12.0, 14.4 Hz, 1H), 1.02–1.81 (m, 6H),
0.92 (t, J = 7.2 Hz, 3H). Compound 2eb; 7.18–7.31 (m, 4H), 5.96 (d, J = 2.3 Hz,
1H), 5.79 (d, J = 2.3 Hz, 1H), 3.03–3.20 (m, 2H), 2.91 (ddd, J = 6.3, 9.8, 16.1 Hz,
1H), 2.64–2.72 (m, 1H), 2.37 (dt, J = 4.6, 13.2 Hz, 1H), 1.85 (dt, J = 4.1, 12.6 Hz,
1H), 0.85–1.40 (m, 4H), 0.78 (t, J = 7.5 Hz, 3H). Compound 2fb; 7.05–7.33 (m,
4H), 5.98 (d, J = 2.3 Hz, 1H), 5.89 (d, J = 2.3 Hz, 1H), 2.97 (dt, J = 10.9, 8.6 Hz,
1H), 2.89 (dt, J = 14.3, 6.4 Hz, 1H), 2.76 (dt, J = 14.4, 8.0 Hz, 1H), 2.46 (ddd,
J = 5.2, 6.9, 12.0 Hz, 1H), 2.25 (ddd, J = 4.0, 12.6, 14.3 Hz, 1H), 2.16 (ddd, J = 4.6,
12.0, 14.3 Hz, 1H), 1.97–2.07 (m, 2H), 0.87–1.34 (m, 4H), 0.84 (t, J = 7.2 Hz, 3H).
Compound 2gb; 7.28–7.42 (m, 5H), 6.01 (d, J = 2.4 Hz, 1H), 5.92 (d, J = 2.4 Hz,
1H), 2.18–2.26 (m, 2H), 2.10 (s, 3H), 1.14–1.45 (m, 4H), 0.93 (t, J = 7.3 Hz, 3H).
Compound 2hb; 7.29 (d, J = 6.9 Hz, 2H), 6.88 (d, J = 6.9 Hz, 2H), 6.04 (d,
J = 2.3 Hz, 1H), 5.90(d, J = 2.3 Hz, 1H), 3.81 (s, 3H), 2.15–2.21 (m, 2H), 2.09 (s,
3H), 1.35–1.44 (m, 2H), 1.13–1.33 (m, 2H), 0.93 (t, J = 7.2 Hz, 3H). Compound
2ib; 7.65 (d, J = 8.6 Hz, 2H), 7.54 (d, J = 8.6 Hz, 2H), 6.15 (d, J = 2.3 Hz, 1H), 6.00
(d, J = 2.3 Hz, 1H), 2.16–2.22 (m, 2H), 2.17 (s, 3H), 1.31–1.42 (m, 2H), 1.08–1.17
(m, 2H), 0.90 (t, J = 7.5 Hz, 3H). Compound 2jc; 7.26–7.39 (m, 5H), 6.07 (d,
J = 2.3 Hz, 1H), 5.91 (d, J = 2.3 Hz, 1H), 2.38 (t, J = 7.5 Hz, 2H), 2.18–2.24 (m, 2H),
1.05–1.80 (m, 8H), 0.93 (t, J = 7.0 Hz, 3H), 0.79 (t, J = 7.0 Hz, 3H). Compound
2kb; 7.42–7.45 (m, 2H), 7.31–7.37 (m, 3H), 6.52 (d, J = 1.5 Hz, 1H), 5.87 (d,
J = 1.5 Hz, 1H), 2.90 (ddd, J = 7.0, 8.0, 18.0 Hz, 1H), 2.64 (ddd, J = 6.5, 7.5,
18.0 Hz, 1H), 1.91–2.05 (m, 2H), 1.60–1.73 (m, 2H), 1.22–1.47 (m, 4H), 0.94 (t,
J = 7.5 Hz, 3H), 0.93 (t, J = 7.5 Hz, 3H). Compound 2lb; 7.37 (s, 4H), 6.04 (d,
J = 2.5 Hz, 2H), 5.92 (d, J = 2.5 Hz, 2H), 2.14–2.25 (m, 4H), 2.12 (s, 6H), 1.34–
1.44 (m, 4H), 1.11–1.32 (m, 4H), 0.92 (t, J = 7.0 Hz, 6H). 1H NMR data of 5
(500 MHz, CDCl3) d 7.66 (d, J = 8.0 Hz, 2H), 7.43 (d, J = 8.0 Hz, 2H), 5.99 (d,
J = 1.2 Hz, 1H), 5.79 (d, J = 1.2. Hz, 1H), 1.90 (ddd, J = 6.3, 9.2, 14.9 Hz, 1H), 1.60
(s, 3H), 1.10–1.37 (m, 4H), 0.80 (t, J = 7.4 Hz, 3H), 0.62 (ddd, J = 6.9, 9.2, 14.9 Hz,
1H).
16. Regarding production of acyclic
a-quaternary a-vinyl carbonyl compounds,
preparation of 2,2-dialkylbut-3-enoates from 4-chloro-2-alkylbut-2-enoates
by the Lewis base-promoted SN20 reaction with alkyl magnesium or zinc
reagents has recently been reported: (a) Lee, Y.; Hoveyda, A. H. J. Am. Chem. Soc.
2006, 128, 15604; (b) Kobayashi, K.; Ueno, M.; Naka, H.; Kondo, Y. Chem.
Commun. 2008, 3780.