Syntheses with organoboranes. X. Monohydroboration of conjugated enynes with catecholborane catalyzed by nickel(II) chloride complexes with diphosphines

Article abstract of DOI:10.1135/cccc19991049

The monohydroboration of representative conjugated enynes - but-1-en-3-yne (1), 2-methylbut-1-en-3-yne (2), pent-3-en-1-yne (3), hex-1-en-3-yne (4), 2-methyl-4-phenyl-but-1-en-3-yne (5), 4-methyl-1-phenylpent-3-en-1-yne (6) and 1-ethynylcyclohex-1-ene (7)

Full text of DOI:10.1135/cccc19991049

Syntheses with Organoboranes
1049
SYNTHESES WITH ORGANOBORANES. X. MONOHYDROBORATION
OF CONJUGATED ENYNES WITH CATECHOLBORANE CATALYZED BY
NICKEL(II) CHLORIDE COMPLEXES WITH DIPHOSPHINES
1
,
2
Marek ZAIDLEWICZ * and Jerzy MELLER
Faculty of Chemistry, Nicolaus Copernicus University, 87-100 Toruń, Poland;
1
2
e-mail: zaidlevi@chem.uni.torun.pl, yogi@chem.uni.torun.pl
Received Jan uary 27, 1999
Accepted April 2, 1999
Dedicated to Dr Stanislav Heřmánek on the occasion of his 70th birthday.
Th e m on oh ydroboration of represen tative con jugated en yn es
– but-1-en -3-yn e (1),
2
-m eth ylbut-1-en -3-yn e (2), pen t-3-en -1-yn e (3), h ex-1-en -3-yn e (4), 2-m eth yl-4-ph en yl-
but-1-en -3-yn e (5), 4-m eth yl-1-ph en ylpen t-3-en -1-yn e (6) an d 1-eth yn ylcycloh ex-1-en e (7),
with catech olboran e in th e presen ce of th e n ickel(II) ch loride com plex with 1,2-bis(diph en yl-
ph osph in o)eth an e gave th e correspon din g 1,3-dien -1-yl organ oboran es in 54–87% yield.
High regioselectivity of th e addition leadin g to th e boron atom at th e 4-position of th e
1
-en -3-yn e system was observed for 1, 2, 3, 6 an d 7.
Key w ord s: Catalytic h ydroboration ; 1,3-Dien -1-yl organ oboran es; 1-En -3-yn es; Catech ol-
boran e; Boron ates; Alkyn es; Nickel.
Catalytic h ydroboration is a n ew m eth odology com plem en tary to th e
2
un catalyzed reaction . Th ese processes often sh ow differen t reactivities,
regio- an d stereoselectivities. Catech olboran e in th e presen ce of rh odium ,
iridium , ruth en ium an d palladium com plexes is th e reagen t m ost often
3
used, alth ough oth er substituted boran es h ave also been applied . Con -
siderin g th e costs, catalysts derived from oth er tran sition m etals are h igh ly
desirable. Recen tly, we discovered th e catalytic activity of n ickel(II) ch loride
an d cobalt(II) ch loride com plexes with 1,2-bis(diph en ylph osph in o)eth an e
(
dppe) an d 1,3-bis(diph en ylph osph in o)propan e (dppp) in th e m on oh ydro-
4
boration of con jugated dien es . Exten din g our studies to oth er con jugated
system s, we turn ed to th e catalyzed h ydroboration of con jugated en yn es as
a poten tial route to 1,3-dien -1-yl organ oboran es. Hayash i an d coworkers
5
described th e reaction of 2-substituted but-1-en -3-yn es with catech olboran e
in th e presen ce of palladium (0) com plexes with m on oden tate an d
biden tate ph osph in e ligan ds – triph en ylph osph in e, dppe, dppb an d dppf.
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

1
050
Zaidlewicz, Meller:
Th e form ation of 1,2- an d 1,4-addition products, depen din g on th e ligan d
structure an d th e m olar ratio of palladium to ligan d, was observed. Here,
th e m on oh ydroboration of represen tative con jugated en yn es
–
but-1-en -3-yn e (1), 2-m eth ylbut-1-en -3-yn e (2), pen t-3-en -1-yn e (3),
h ex-1-en -3-yn e (4), 2-m eth yl-4-ph en ylbut-1-en -3-yn e (5), 4-m eth yl-
1
-ph en ylpen t-3-en -1-yn e (6) an d 1-eth yn ylcycloh ex-1-en e (7), with
catech olboran e in th e presen ce of n ickel(II) ch loride com plex with dppe is
described.
EXPERIMENTAL
1H, 13C an d 11B NMR spectra were recorded on Varian Gem in i 200 an d Varian In ova 500
spectrom eters. High resolution m ass spectra were recorded on a AMD 604 in strum en t. All
glassware was dried for several h ours in an oven at 120 °C, assem bled h ot an d cooled in an
6
argon atm osph ere. Catech olboran e was prepared accordin g to th e literature procedure ,
7
stirred with a sm all am oun t of h ex-1-en e for 3 h , an d distilled. Th e en yn es 1–7 (ref. ),
8
9
8
9
NiCl (PPh ) (ref. ), NiCl (dppe) (ref. ), NiCl (dppp) (ref. ), CoCl (dppe) (ref. ) an d
2
3
2
2
2
2
1
0
CoCl (dppp) (ref. ), were prepared accordin g to th e literature. Th e en yn e 3 was an E/Z m ix-
2
ture 43 : 57. NiCl (PPh ) was also obtain ed from
a com m ercial source (Aldrich ).
2
3 2
Tetrah ydrofuran was distilled from sodium ben zoph en on e ketyl prior to use. Meltin g poin ts
are un corrected.
(
E)-2-(3-Meth ylbuta-1,3-dien -1-yl)ben zo[1,3,2]dioxaborole (2a). Gen eral Procedure for th e
Mon oh ydroboration of 1,3-En yn es
Catech olboran e (3.00 g, 25 m m ol) was added to a m ixture of NiCl (dppe) (0.132 g, 0.25
2
m m ol), 2-m eth ylbut-1-en -3-yn e (2.00 g, 30 m m ol) an d tetrah ydrofuran (20 m l) at room
tem perature un der argon atm osph ere. Th e m ixture was stirred at room tem perature an d
1
1
m on itored by B NMR an alysis. After 8 h th e catech olboran e sign al at δ 28.0 ppm disap-
peared. Th e solven t was rem oved an d 2a was isolated by distillation , 2.75 g (59%), b.p.
9
1–93 °C/0.2 m m Hg. 1H NMR (CDCl ): 1.95 s, 3 H (CH ); 5.35 s, 2 H (H-4); 5.90 d, 1 H,
3
3
J(1,2) = 18.2 (H-1); 7.11 m , 2 H (H-Ar); 7.25 m , 2 H (H-Ar); 7.49 d, 1 H, J(1,2) = 18.2 (H-2).
1
3
C NMR (CDCl ): 17.58 q, 112.36 d, 121.82 t, 122.62 d, 142.92 s, 148.39 s, 154.73 d. HR
3
1
1
MS, for C11H11O2 B calculated: 186.08521; foun d: 186.08670. For C11H11O B (186.0) calcu-
2
lated: 71.03% C, 5.96% H; foun d: 70.83% C, 5.87% H.
(
E)-2-(Buta-1,3-dien-1-yl)benzo[1,3,2]dioxaborole (1a). 1H NMR (CDCl ): 5.42 d, 1 H, J(3,4a) =
3
1
1
0.2 (H-4a); 5.54 d, 1 H, J(3,4b) = 17.6 (H-4b); 5.92 d, J(1,2) = 17.6 (H-1); 6.55 dt, J(3,4a) =
0.2, J(3,4b) = 17.6 (H-3); 7.11 m , 2 H (H-Ar); 7.25 m , 2 H (H-Ar); 7.37 dd, 1 H J(2,3) = 10.3,
1
3
J(1,2) = 17.8 (H-2). C NMR (CDCl ): 112.39 d, 122.69 d, 122.76 t, 138.58 d, 148.40 s,
3
1
52.53 d.
1E,3E/Z)-2-(Penta-1,3-dien-1-yl)benzo[1,3,2]dioxaborole (3a/ 3b) isolated as an E/Z mixture
(
1
1
4
3 : 57. HR MS, for C11H11O2 B calculated: 186.08521; foun d: 186.08613. For C11H11O B
2
(
186.0) calculated: 71.03% C, 5.96% H; foun d: 70.73 % C, 5.83% H.
1E,3E)-isom er 3a: 1H NMR (500 MHz, CDCl ): 1.88 d, 3 H, J(4,5) = 7.0 (H-5); 5.77 d, 1 H,
(
3
J(1,2) = 17.5 (H-1); 6.09 dq, 1 H, J(3,4) = 16.2, J(4,5) = 7.0 ( H-4); 6.24–6.33 m , 1 H (H-3);
7
.10 m , 2 H (H-Ar); 7.25 m , 2 H (H-Ar); 7.37 dd, 1 H, J(1,2) = 17.5, J(2,3) = 10.5 (H-2).
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Syntheses with Organoboranes
1051
1
3
C NMR (CDCl ), a m ixture of 3a an d 3b: 13.37 q, 17.82 q, 111.82 d, 111.87 d, 122.08 d,
3
1
22.15 d, 130.93 d, 132.16 d, 133.31 d, 135.76 d, 146.36 d, 147.97 s, 152.21 d.
1E,3E)-isom er 3b: 1H NMR (CDCl ): 1.95 d, 3 H, J(4,5) = 7.4 (H-5); 5.85 dq, 1 H, J(3,4) =
(
3
1
0.5, J(4,5) = 7.4 (H-4); 5.89 d, 1 H, J(1,2) = 18.0 (H-1); 6.24–6.33 m , 1 H (H-3); 7.10 m , 2 H
(
H-Ar); 7.25 m , 2 H (H-Ar); 7.76 dd, 1 H, J(1,2) = 17.5, J(2,3) = 10.5 (H-2).
Z)-2-(Hexa-1,3-dien-4-yl)benzo[1,3,2]dioxaborole (4a) and (Z)-2-(Hexa-1,3-dien-3-yl)benzo-
1,3,2]dioxaborole (4b) isolated as a 4a/ 4b mixture 66 : 34. For C12H13O B (200.0) calculated:
(
[
2
7
2.05% C, 6.55% H; foun d: 72.32% C, 6.79% H.
1
Com poun d 4a: H NMR (500 MHz, CDCl ): 1.19 t, 3 H J(5,6) = 7.6 (H-6); 2.56 q, 2 H,
3
J(5,6) = 7.6 (H-5); 5.45 d 1 H, J(1a,2) = 10.0 (H-1a); 5.57 d, 1 H, J(1b,2) = 16.7 (H-1b);
.82–6.94 m , 1 H (H-2); 7.12 m , 2 H (H-Ar); 7.21 d, 1 H, J(3,4) = 11.3 (H-3); 7.28 m , 2 H
6
1
3
(
H-Ar). C NMR (CDCl ): 14.94 q, 21.94 t, 112.37 d, 122.21 t, 122.60 d, 132.29 d, 144.67 d,
3
1
48.60 s.
Com poun d 4b: 1H NMR (500 MHz, CDCl ): 1.17 t, 3 H, J(5,6) = 7.5 (H-6); 2.46 quin tet,
3
2
6
1
H, J(5,6) = 7.6 (H-5); 5.40 d, 1 H, J(1a,2) = 11 (H-1a); 6.00 d, 1 H, J(1b,2) = 18.0 (H-1b);
1
3
.82–6.94 m , 2 H (H-2, H-4); 7.12 m , 2 H (H-Ar); 7.28 m , 2 H (H-Ar). C NMR (CDCl ):
3
3.36 q, 22. 39 t, 112.37 d, 118.23 t, 122.60 d, 132.76 d, 148.60 s, 153.13 d.
1
(
Z)-2-(4-Methyl-1-phenylpenta-1,3-dien-1-yl)benzo[1,3,2] dioxaborole (6a). H NMR (CDCl ):
3
1
7
.95 s, 3 H (CH ); 2.17 s, 3 H (CH ); 6.43 d, 1 H, J(2,3) = 11.4 (H-3); 7.16–7.21 m , 2 H (H-Ar)
3 3
.35–7.39 m , 2 H (H-Ar); 7.56–7.60 m , 5H (H-Ar) 7.93 d, 1 H, J(2,3) = 11.4 (H-2). C NMR
1
3
(
CDCl ): 18.85 q, 26.67 q, 112.43 d, 122.59 d, 123.05 d, 126.67d, 128.23 d, 129.64 d, 139.39 s,
3
1
42.42 d, 144.03 s, 148.77 s.
E)-2-[2-(Cyclohex-1-en-1-yl)ethenyl]benzo[1,3,2]dioxaborole (7a ). 1H NMR (CDCl ):
(
3
1
1
.64–1.74 m , 4 H (CH ); 2.22–2.27 m , 4 H (CH ); 5.75 d, 1 H, J(1,20) = 18.4 (H-1); 6.12 m ,
2 2
H (H-4); 7.07 m , 2 H (H-Ar); 7.23 m , 2 H (H-Ar); 7.40 d, 1 H, J(1,2) = 18.4 (H-2). C NMR
1
3
(
CDCl ): 22.12 t, 22.17 t, 23.66 t, 26.18 t, 112.15 d, 122.38 d, 136.20 d, 137.18 s, 148.40 s,
3
1
55.67 d. For C14H15O B (226.1) calculated: 74.38% C, 6.69% H; foun d: 74.50%C, 6.62% H.
2
1
-Meth yl-4-oxo-2-exo-ph en yl-3-oxabicyclo[3.3.1]n on -7-en e-6-endo-carboxylic acid (8)
A solution of 2a (2.98 g, 16 m m ol) an d m aleic an h ydride (1.57 g, 16 m m ol) in toluen e
(
(
20 m l) was kept at 80 °C for 3 h . After coolin g to 0 °C, fresh ly distilled ben zaldeh yde
1.70 g, 16 m m ol) was added. Th e m ixture, wh ich solidified, was allowed to reach room
tem perature an d th en it was warm ed to 80 °C. Water (1.5 m l) was added an d th e m ixture
was kept at 80 °C for 0.5 h . Toluen e was rem oved un der vacuum , th e solid was wash ed with
dieth yl eth er (20 m l) an d crystallized from aceton itrile (25 m l) to give 8, 3.12 g (71%), m .p.
2
40–242 °C (ref.11 gives m .p. 242–243 °C).
RESULTS AND DISCUSSION
Nickel(II) ch loride an d cobalt(II) ch loride com plexes with triph en yl-
ph osph in e, dppe an d dppp were used as catalysts. Th e stability of 1 M
catech olboran e solution in tetrah ydrofuran in th e presen ce of 1 m ole % of
th ese com plexes was m on itored by 11B NMR. For all th e com plexes, th e
catech olboran e sign al at δ 28.0 ppm rem ain ed th e m ajor sign al after 24 h at
room temperature. No signal at δ 1.0 ppm corresponding to borane–tetrahydrofuran,
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

1
052
Zaidlewicz, Meller:
a possible disproportionation product, was observed. A signal at δ 18.8 ppm in tegratin g
for 10–12% of th e total area of th e sign als was presen t after 6 h an d was n ot
furth er in creasin g at a lon ger tim e. Its ch em ical sh ift correspon ds to a bo-
rate ester. Th e h ydroboration of 2-m eth ylbut-1-en -3-yn e (2) with
catech olboran e in th e presen ce of th e com plexes sh own in Table I was
1
1
m on itored by B NMR.
As follows from th e data presen ted in Table I, on ly two types of products
were form ed. In addition to a sign al at δ 31–32 ppm correspon din g to th e
h ydroboration product, a sign al at δ 18–20 ppm correspon din g to a borate
ester was observed. Nickel(II) ch loride in th e presen ce of various am oun ts
of triph en ylph osph in e sh owed low activity. Sim ilarly, th e com m ercial
TABLE I
Hydroboration products of 2-m eth ylbut-1-en -3-yn e with catech olboran e (m olar ratio 1 : 1)
in th e presen ce of NiCl2 or CoCl2 com plexes with ph osph in es at room tem perature in
tetrah ydrofuran
11B NMR δ, ppm (con ten t, %)b
Tim e
h
Catalysta
un reacted
catech olboran e
h ydroboration
product
oth er products
NiCl /PPh
10
10
10
8
26.60
(56.0)
32.09
(27.1)
20.15
(16.9)
2
3
3
3
1
: 1
NiCl /PPh
26.35
(52.5)
31.96
(27.1)
19.82
(20.4)
2
1
: 2
NiCl /PPh
25.46
(49.5)
30.92
(23.9)
19.06
(26.6)
2
1
: 4
NiCl (PPh )
3 2
26.25
31.94
(21.6)
19.63
(25.8)
2
(
52.6)
NiCl (dppe)
8
31.81
18.59
(11.8)
2
(
88.2)
31.16
84.8)
NiCl (dppp)
8
18.15
(15.2)
2
(
CoCl (dppe)
8
26.19
77.3)
30.65
(15.2)
19.52
(7.5)
2
(
CoCl (dppp)
8
26.31
43.5)
31.87
(34.5)
19.63
(22.0)
2
(
a
m ole %; b calculated from th e sign al area.
1
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

Syntheses with Organoboranes
1053
NiCl (PPh ) com plex was of low activity. In th e presen ce of th ese com -
2
3 2
poun ds, on ly 24–27% of th e h ydroboration product was form ed after 24 h .
In con trast, th e h ydroboration reaction in th e presen ce of n ickel(II) ch lo-
1
1
ride com plexes with dppe or dppp was com plete in 8 h , th e B NMR spec-
trum in dicatin g 88.2 or 84.8% of th e h ydroboration products, respectively.
Th e activity of th e correspon din g cobalt(II) ch loride com plexes was m uch
lower. Con sequen tly, th e m ost active NiCl (dppe) was selected for furth er
2
experim en ts. Th us, th e h ydroboration of represen tative acyclic an d cyclic
con jugated en yn es 1–7 at th e m olar ratio 1 : 1, in th e presen ce of 1 m ole %
NiCl (dppe), was carried out at room tem perature in tetrah ydrofuran
2
1
1
(
Sch em e 1), m on itorin g th e reaction by B NMR. Th e organ oboran e prod-
ucts were isolated by distillation an d an alyzed by H an d C NMR. Th e re-
sults are presen ted in Table II.
1
13
3
O
R
3
2
1
O
O
R
B
R
R
NiCl (dppe)
2
O
+
HB
2
1
R
R
R
R
1-7a/b
1
-7
1
2
3
R
R
R
R
H
1
2
3
4
5
6
7
H
H
H
H
H
H
H
H
COOH
H
H C
3
CH3
H
(
i)
CH3,H
O
2
a
H
H
H
H
H
H
CH2CH3
O
Ph
CH3
H
Ph
Ph
H
CH3
H
CH3
8
-(CH2)4-
(
i) 1. maleic acid anhydride, 2. benzaldehyde
SCHEME 1
Th e m on oh ydroboration of but-1-en -3-yn e (1) was com plete in 10 h . Th e
product readily isolated by distillation is of lim ited stability becom in g a
glassy solid in a few h ours at room tem perature. A m oderate 53% yield is
m ost probably due to partial oligom erization of th e product durin g distilla-
1
13
tion . Th e H an d C NMR spectra of th e fresh ly distilled product in dicate
E)-2-(buta-1,3-dien -1-yl)ben zo[1,3,2]dioxaborole (1a). It is in terestin g to
(
n ote th at th e reactivity of 1a in th e Diels–Alder reaction with tetra-
cyan oeth ylen e was lower com pared with buta-1,3-dien e. Th e dien e reacted
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

1
054
Zaidlewicz, Meller:
TABLE II
Hydroboration products of con jugated 1-en -3-yn es with catech olboran e (m olar ratio 1 : 1) in
th e presen ce of NiCl (dppe) at room tem perature in tetrah ydrofuran
2
Hydroboration products
Tim e
En yn e
h
con ten tb,c
11B NMR yieldd
b.p.
°C/m m Hg
structurea
%
δ, ppm
%
1
2
10
8
Bc
(1a)
(2a)
>95
>95
78–80/1.0
91–93/0.2
33.26
54
Me
31.49
33.96
59
79
Bc
3e
8
Me
(3a)
(3b)
43
57
88–90/0.1
Bc
Bc
Bc
Me
Et
4
8
(4a)
66
81–82/0.02
31.31
78
Et
(
4b)
34
Bc
f
5
6
24
24
Ph
Me
g
(6a)
(7a)
>95
>95
31.49
31.79
Bc
Me
7
8
136–138/0.07
87
Bc
O
a
Bc
=
B
; b by 1H NMR; c in CDCl3; d isolated; e th e startin g en yn e 3 was an E/Z
O
m ixture 43 : 57; n ot isolated, on ly 30% of catech olboran e reacted; g n ot distilled.
f
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

Syntheses with Organoboranes
1055
1
2
in 1 h at room tem perature in tetrah ydrofuran as reported earlier , wh ereas
1
1
n o reaction with 1a un der th e sam e con dition s was observed by B NMR.
Th e m on oh ydroboration of 2-m eth ylbut-1-en -3-yn e (2) was com plete in
8
h . Th e product 2a form ed with h igh regioselectivity was isolated by distil-
lation in 59.1% yield. It was m ore stable com pared to 1a an d readily re-
acted with m aleic an h ydride to give th e correspon din g Diels–Alder adduct,
furth er tran sform ed in to th e addition product 8 on reaction with
1
1
ben zaldeh yde . In con trast to th e palladium catalyzed h ydroboration of
-substituted 1-en -3-yn es leadin g to 1,2- an d 1,4-addition products depen d-
2
in g on th e reaction con dition s, n o 1,4-addition was observed in th e pres-
en ce of n ickel(II) ch loride com plexes used in th is study. Sim ilarly, th e
en yn es 3 an d 7 h avin g a term in al triple bon d were h ydroborated with h igh
regioselectivity to place th e boron atom at th e term in al position . Clearly,
th e substitution pattern of th e double bon d h as n o effect on th e course of
addition to th e term in al triple bon d in 1–3 an d 7.
Th e en yn e 4 reacted in 8 h to give a m ixture of 4a an d 4b in 78.4% yield.
5
In con trast to th e palladium -catalyzed h ydroboration , alkyl substitution at
th e 4-position of th e en yn e system does n ot in h ibit th e addition . However,
th e ph en yl substituen t at th e 4-position h as a rate-retardin g effect. Both
ph en yl substituted en yn es 5 an d 6 reacted m uch slower com pared with th e
alkyl substituted 4. Th e reaction with 5 was very sluggish an d after 24 h
on ly 30% of catech olboran e was con sum ed. Th e en yn e 6 reacted com -
pletely in th e sam e tim e in dicatin g th at th e substitution pattern of th e dou-
ble bon d in fluen ces th e reactivity of th e ph en yl substituted triple bon d.
Th e addition to 6 is regioselective affordin g 6a with th e boron atom placed
at th e ph en yl substituted carbon atom .
In con clusion , th e m on oh ydroboration of con jugated 1-en -3-yn es 1–4, 6
an d 7 with catech olboran e, in th e presen ce of n ickel(II) ch loride com plex
with dppe proceeds un der m ild con dition s to give th e correspon din g
1
,3-dien -1-yl organ oboron ates in 53–87% yields. Mild reaction con dition s
en able th e syn th esis of labile products, e.g., th e buta-1,3-dien -1-yl
catech olboran e derivative 1a, n ot readily available by oth er m eth ods. Th e
1
,2-addition products were obtain ed exclusively, regardless of th e substitu-
tion pattern of th e en yn e system . High regioselectivity of th e addition to
en yn es with term in al triple bon ds is observed, wh ereas for in tern al triple
bon ds, th e direction of addition an d reactivity depen d, on th e substituen ts
of th e en yn e system .
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

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056
Zaidlewicz, Meller:
The work was supported by grant No. 3T09A 13809 from the State Committee for Scientific
1
Research, Poland. The authors thank Prof. L. Kozerski for the H NMR spectra taken on a 500 MHz
instrument.
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