Notes: Formation of Cyclopropane Derivatives from 4-Bromocrotonic Esters (original) (raw)
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The Journal of Organic Chemistry, 1991
The verbenone-derived cyclopentadienyl compound ( 1S,8S)-7,7,9,9-tetramethyltricyclo[6.1.1.02~6]deca-2,fi-dienyllithium (VCpLi) yielded a 3:2 mixture of exo and endo deuterio quench products upon reaction with DzO at -78 "C in THF. Stereochemical identification was achieved by NMR analysis of Diels-Alder addition products. Reaction of VCpLi with Me3SiC1 under the same Conditions gave rise to a 9:l exo:endo product mixture. Silatropic shifts were observed in these quench products. According to NMR analysis, VCpLi consists nearly exclusively of the exo-Li monomer in THF at +26 "C. However, at -80 "C a ternary equilibrium of an exo-Li monomer, an exo,exo-Li sandwich dimer, and an endo,endo-Li sandwich dimer in a 5.1:2.8:1.0 molar ratio has been detected. Thermodynamic parameters for the monomer-dimer equilibrium are AH" = -3.6 f 0.2 kcal/mol and ASo = -15.6 f 0.9 eu. Due to ring current effects, unusual upfield 6Li chemical shifta are observed: 6 (ppm) = -7.83 (exo monomer), -12.22 (exo,exo dimer), and -12.25
Journal of Organic Chemistry, 1987
reported to give only p-anomers. The desired compound 3 was also the major product of glycosylation of the 6bromopurine 1, although the minor component was apparently the 9-CY isomer rather than the expected 7-0 isomer. In addition, the facile and direct isolation of the 9-P-deoxyribofuranosyl isomers precludes lengthy chromatographic separation of glycosylation products. In the final step, the protected 2,6-dihalo nucleosides are converted nearly quantitatively to the target 2-halo-2'deoxyadenosines. This chemical method appears to be adaptable to large-scale syntheses, as demonstrated by the 50-fold greater scale of the glycosylation of 2,6-dibromopurine as compared with the enzymatic glycosylation of 2-br0moadenine.~
Organometallic reagents in organic synthesis—V
Tetrahedron, 1979
Theprefenxlceforc&lgateadditioninrca&nlsof oqanocoprata~ &CuLii with a,@unsrturated ketones (scheme1)ha8bl!enwiddyexploitedinorganicsyll-thc3ia:Themechanismof&i8rl!actkmhasreceived some atta&n' however, to date, a comprd1cn8ive mecbaaiam baa not evolved. we were iotercsted in exam&g tJle stereochemistry of orgawcoprate coo-jItgateeddsons,and~thisstndybecameiuvolved in conskleration of several mechansc featuns of the nsctkwl. Herein we report the reslllta of this involvement. ThemoatQotablefeatIwofthec&lgateadditkm WithR&UIipnthatthCreactionpKUhUX8alleaokte aaion'alJinitialproductandtber~~ofth~ sz ~&v~yR2Qu " reta&L mnactlve towards satuwed calbonyl compouls and collaideration of th~CE8Ult8llXdtotheproposalJofaUdectroPtransfCI processocwringdor&conjugateaddSm.Ardatkm-shipb&vecntbesnccessofconju@eadd&aandthe abilityofthe uaatwated ketone to accept electrons, aa measured by redwtkm potential8 (I&), haa evolved which is in accordance with the dectron transfer mecha&ic wnccpt.
Organometallics, 1990
The reaction between allylstannanes and &unsaturated acyliron complexes has been examined. When the reaction is conducted in the presence of Lewis acids, [3 + 21 cycloaddition products are obtained with extremely high degrees of stereoselectivity. If the iron complex is alkylated prior to addition of the allylstannane, products resulting from the Michael addition of allyl anion are obtained. The [3 + 21 cycloadducts contain acyliron and organotin functionalities. The acyliron group is easily converted to the corresponding ester by treatment with N-bromosuccinimide in the presence of alcohols. The tributyltin group can be converted to a hydroxy group by treatment with bromine followed by treatment with peracids and amine bases; this transformation occurs with complete retention of stereochemistry. The high stereoselectivity can be explained by reaction through a synclinal orientation of allylstannane and the acyliron complex. The question of allylation vs cycloaddition has been attributed to the relative reactivity of the intermediate enolate derivatives. Dedicated to the memory of Professor John K. Stille. 0276-7333/90/2309-3157$02.50/0 Scheme I R3 R7 1 2 (1) Some of these studies have been reported in preliminary form: (a) Herndon, 15D 15A 20A 208 20c HA 63.84, q, J = 6.0 HZ HA 64.46, rn HA 63.69, HA 63.60, HA 63.92, q, J = 5.3 HZ q, J = 4.7 HZ rn, W112 = 6 HZ Figure 1. Spectral comparison for compound 15D and selected compounds. 15F HA 63.19 1, J = 4.9 HZ 15F-PNB HA 64.72 HE 62.19 dd, J = 5.8, 4.6 HZ 1, J = 9.8 HZ 20D 20E 20F 20G 20H HA 62.97 HA 63.53 HA 63.48 HA 63.68 HA 63.77 1, J = 8.0 HZ t, J = 8.0 HZ 1, J = 5.0 HZ dd, J = 5.2, 5.0 HZ dd, J = 3.4, 3.0 Hz