| Summary: | A new synthetic method, involving the copper(I) mediated intramolecular conjugate
addition of alkenyltrimethylstannanes to α,(β-unsaturated ketones, has been developed.
Alkylated vinylogous esters of general structure 338 were prepared from vinylogous ester 120
and allylic bromide 128; these compounds were readily transformed via either reduction or
Grignard addition, followed by hydrolysis and dehydration, into enones of general structure 150.
Upon treatment with 2.5 equiv of CuCl in DMF, these enones afforded the functionalized
bicyclo[4.3.0]non-8-en-3-ones having general structure 151. Enones 150 possessing sterically
bulky R² groups gave poor yields when cyclized with CuCl; however, the use of CuCN in
DMSO ameliorated this problem and produced superior results.
Using a similar procedure, enones of general structure 46 were prepared from 189 (R³ =
H or Me) and Afunctional reagents of general structure 190. Upon treatment with 2.5 equiv of
CuCN in DMSO, enones 46 were converted into the corresponding bicyclic compounds 47.
Subsequent intramolecular alkylation with potassium tert-butoxide in DMSO afforded the
tricyclic ketones having general structure 48. Particularly noteworthy was the synthesis by this
method of ketone 244, which possesses three contiguous quaternary centres.
Using analogous procedures, dienones 251 and 51 were prepared from 120 and alkylating
agents 128 and 190 via sequential bis-alkylation, reduction, hydrolysis/dehydration and
dehydrogenation. Under the same conditions as described above (CuCN, DMSO), these
substrates underwent one-pot tandem conjugate addition reactions to give tricyclic compounds
269 and 52, respectively. Interestingly, when cyclization of 251 was conducted in a sealed tube,
the bridged structure 288 was formed as the major product. Treatment of chloro ketones 52 (n =
1, 2) with t-BuOK in DMSO resulted in tandem intramolecular alkylations to provide the
pentacyclic compounds of general structure 53; similar attempts to cyclize 52 (n = 3) gave
complex mixtures.
A new, stereospecific CuCl-mediated intermolecular oxidative coupling reaction of
alkenyltrialkylstannanes was also discovered, whereby (E)- and (Z)-3-trimethylstannylalk-2-
enoates (90 and 92) as well as alkenylstannanes 365 were converted into conjugated dienes of
general structure 91, 93, and 366, respectively, by treatment with 2.5 equiv of CuCl in DMF.
New methods were also developed for the conversion of alkyl (Z)- and (E)-2,3-
bis(trimethylstannyl)alk-2-enoates (102 and 103, respectively) into the E and Z isomers of the
corresponding alkyl 3-trimethylstannylalk-2-enoates (90 and 92, respectively). Treatment of 102
with a catalytic amount of CuCl in DMF/H₂O afforded stereoselectively the E alkenoates 90,
whereas treating either 102 or 103 with 1.2 equiv of IN aqueous HC1 in DMF afforded primarily
the Z isomers 92.
[chemical compound diagrams]
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