ORGANIC
LETTERS
2010
Vol. 12, No. 11
2622-2625
Borostannylation of Alkynes and
Enynes. Scope and Limitations of the
Reaction and Utility of the Adducts
Ramakrishna Reddy Singidi and T. V. RajanBabu*
Department of Chemistry, The Ohio State UniVersity, 100 West 18th AVenue,
Columbus, Ohio 43210
Received April 11, 2010
ABSTRACT
The utility of the hetero-bismetallating reagent 1,3-dimethyl-2-trimethylstannyl-2-bora-1,3-diazacyclopentane (1) has not been fully realized
because of the hydrolytic instability of the products derived from catalyzed vicinal syn-additions to alkynes. The isolation of a variety of such
adducts derived from alkynes (and also from hitherto unreported additions to 1,3-enynes) as stable boron pinacolates is reported. Examples
of the applications of resulting products in tandem cross-coupling reactions and as dienes in Diels-Alder reactions are illustrated.
While exploring the applications of hetero-bismetallative
cyclization of R,ω-diynes using 1,3-dimethyl-2-trimethyl-
stannyl-2-bora-1,3-diazacyclopentane 1 (eq 1) in the synthesis
of highly functionalized dibenzocyclooctadienes,1 it became
apparent that except for low molecular weight adducts where
the products can be isolated by distillation, or in rare cases
where they are crystalline, the hydrolytic instability of the
primary [BSn] adducts severely limits the utility of this
otherwise useful reagent.2 Further impetus for work in the
area came from our recent recognition that, despite the
extreme sensitivity to moisture and difficulties in its prepara-
tion, this reagent could have a much broader substrate scope
and improved selectivity in its reactions as compared to the
more well-known silylstannanes.3 Even though both reagents
undergo regio- and stereoselective 1,2-addition to terminal
alkynes, giving products in which the stannyl residue is
attached to the internal carbon, only the [BSn] reagent reacts
with internal alkynes. In this paper, we provide examples of
a simple protocol for the isolation of the borylstannyl alkenes
derived from acetylene, mono- and disubstituted alkynes, and
enynes. Also illustrated are examples of applications of the
products derived from these reactions, including tandem
Stille/Suzuki coupling reactions and the use of a highly
(1) Singidi, R. R.; RajanBabu, T. V. Org. Lett. 2008, 10, 3351.
(2) Palladium-catalyzed additions of 1 to alkynes including reactions
that lead to carbocyclic 1,2-bisalkylidenes were initailly reported by Tanaka
et al. See: (a) Onozawa, S.-y.; Hatanaka, Y.; Sakakura, T.; Shimada, S.;
Tanaka, M. Organometallics 1996, 15, 5450. (b) Onozawa, S.-y.; Hatanaka,
Y.; Choi, N.; Tanaka, M. Organometallics 1997, 16, 5389. See also: (c)
Weber, L.; Wartig, H. B.; Stammler, H. G.; Stammler, A.; Neumann, B.
Organometallics 2000, 19, 2891. For the preparaion of the reagent 1, see:
(d) Niedenzu, K.; Rothgery, E. F. Synth. React. Inorg., Met.-Org. Chem.
1972, 2, 1. For a review of 1,3-dimethyl-2-trimethylstannyl-2-bora-1,3-
diazacyclopentane, see: (e) Tanaka, M. In Encyclopedia of Reagents for
Organic Synthesis; Paquette, L. A., Ed.; John Wiley: New York, 2004.
(3) (a) Chenard, B. L.; Laganis, E. D.; Davidson, F.; RajanBabu, T. V.
J. Org. Chem. 1985, 50, 3666. (b) Warren, S.; Chow, A.; Fraenkel, G.;
RajanBabu, T. V. J. Am. Chem. Soc. 2003, 125, 15402. (c) Kumareswaran,
R.; Shin, S.; Gallou, I.; RajanBabu, T. V. J. Org. Chem. 2004, 69, 7157.
(d) Apte, S.; Radetich, B.; Shin, S.; RajanBabu, T. V. Org. Lett. 2004, 6,
4053. (e) Trimethylsilyltributylstannane: RajanBabu, T. V.; Shin, S. In
Encyclopedia of Reagents for Organic Synthesis; Paquette, L. A., Ed.; John
Wiley: New York, 2005.
10.1021/ol100824f 2010 American Chemical Society
Published on Web 05/11/2010