[19312-27-5]  · C10H22Sn2  · 2,3-Bis(trimethylstannyl)-1,3-butadiene  · (MW 379.66)

(synthon for the 2,3-dianion of 1,3-butadiene)

Physical Data: low-melting solid, bp 65-66 °C/0.8 mmHg (distillation); stable indefinitely at -20 °C under nitrogen

Preparative Methods: 1 treatment of either 2,3-dichloro-1,3-butadiene or commercially available 1,4-Dichloro-2-butyne with 2 equiv Trimethylstannyllithium in THF affords 1,4-bis(trimethylstannyl)-2-butyne as the kinetic product. This alkyne can be isomerized to 2,3-bis(trimethylstannyl)-1,3-butadiene by a catalytic amount of either Methyllithium or trimethylstannyllithium and 2 equiv of HMPA in THF (eq 1). Therefore either dihalide can serve as precursor to either stannane. A one-pot synthesis can be accomplished in 70% yield. It may be advantageous to prepare the trimethylstannyllithium reagent with lithium wire containing 1% sodium.2

Handling, Storage, and Precautions: organotin compounds should be considered toxic and should be handled with appropriate care.

Lithium Reagents.

The divergence of kinetic and thermodynamic control among lithium reagents derived from Sn/Li transmetalation of 2,3-bis(trimethylstannyl)-1,3-butadiene can have profound synthetic implications (eqs 2 and 3). The monolithiated butadiene is less stable than the isomeric lithiated allene; their common dilithio species appears to be propargylic. Thus 2-lithio-3-(trimethylstannyl)-1,3-butadiene can furnish diene products, alkyne products, or mixtures depending on whether the lithium reagent is handled under strictly kinetic conditions or is allowed to equilibrate.

Monosubstitution Reactions.

A solution of 2-lithio-3-(trimethylstannyl)-1,3-butadiene is prepared at -78 °C in THF and then transferred by cannula (jacketed, -78 °C) to a solution of electrophile in THF, ether, or pentane at -78 °C. In this manner, silicon halides, positive halogen sources, sulfenylating reagents, primary alkyl halides, some secondary alkyl halides, elemental selenium, and carbon dioxide afford good yields of monosubstitution products.

When the 2-lithio-3(trimethylstannyl)-1,3-butadiene reacts with simple carbonyl electrophiles (eq 4; M = Li), diene products predominate with varying amounts of contamination by allenic substitution. If the lithiobutadiene is first transformed to the Grignard reagent by exchange with Magnesium Bromide (eq 4; M = MgBr), allenes are obtained.

The most effective organocopper species for conjugate addition reactions is derived from 2-lithio-3-(trimethylstannyl)-1,3-butadiene using Copper(I) Iodide-Tributylphosphine. The reaction yield of 64% is based on chalcone (eq 5). No allenic products are formed, but the Gilman reagent requires 2 equiv lithiobutadiene.

Disubstitution Reactions.

Since Sn/Li transmetalation of the stannylated butadienes is faster than the reaction of many electrophiles with methyllithium, some double derivatizations can be carried out in situ by simply adding 2-3 equiv of MeLi to a solution of 2,3-bis(trimethylstannyl)-1,3-butadiene and 2 equiv of electrophile in THF at -78 °C. Silicon halides, elemental selenium, and primary iodides are appropriate electrophiles for such reactions. Sequential disubstitution reactions may be carried out providing the first substituent is stable to methyllithium in THF.

Diels-Alder Reactivity.

Compared to the parent butadiene (krel = 1), 2,3-bis(trimethylstannyl)-1,3-butadiene is a poor Diels-Alder diene (krel = 0.05).

1. Reich, H. J.; Reich, I. L.; Yelm, K. E.; Holladay, J. E.; Gschneidner, D. JACS 1993, 115, 6625.
2. Reich, H. J.; Yelm, K. E.; Reich, I. L. JOC 1984, 49, 3438.

Larry C. Blaszczak

Lilly Research Laboratories, Indianapolis, IN, USA

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.