5-Lithio-2,3-dihydrofuran

Hetero-l,l-dimetallo-l-alkenes and hetero-1,1-dihalo-1-alkenes could be obtained in a stereoselective manner from 2-lithio-2,3-dihydrofuran via a dyotropic-type rearrangement of the derived cuprate. An example is depicted below <03SL955> <03S2530>. 

Lithio-l-methoxyallene 183 ° , readily accessible by deprotonation of methoxyal-lene with n-butyllithium in diethyl ether, turned out to be a versatile C-3 building blocL It adds to aldehydes and ketones giving hydroxyaUcylated allenes 184, which undergo a ring-closure reaction under basic conditions. Thus, 3-methoxy-2,5-dihydrofurans 185 are obtained. Subsequent acid hydrolysis leads to the formation of dihydro-3(2//)-... 

Table 24 I3C NMR Parameters0 for 2,3-Dihydrofuran and its 5-Lithio and -Deutero Derivatives <80joc49S9>...

The reaction of o-lithio-a-methoxyallene with cyclopentanone gives an allenic carbinol. Treatment of this material with potassium r-butoxide in r-butyl alcohol containing 18-crown-6 heated at reflux for 15 h provides the dihydrofuran derivative, which, after acid hydrolysis, gives a spirodihydrofuranone. The method has been utilized as an iterative process for the synthesis of helical molecules (Scheme 16). ... 

On treatment with LDA, methyl 1-trimethylsilylallenyl ether isomerizes to methyl 3-lithio-l-trimethyl-silylpropargyl ether, which can be used efficiently for the preparation of l-methoxy-l-alken-3-ynes and 2-methoxy-2,5-dihydrofurans. The isomerization in the first step may proceed through a sequence of deprotonation and protonation processes with LDA and diisopropylamine, respectively, since it does not take place under the influence of butyllithium (Scheme 21). ... 

Dialkyl-1-lithio-l-phenylthioallenes add efficiently to ketones only on warming to -20 C or above the adducts are readily cyclized by acid, or several other electrophiles, to produce highly substituted 2,S-dihydrofurans (Scheme 23). ... 

Metallation of 2,3,4,5-tetrahydrooxepin with Bu"Li or Bu Li leads to 7-lithio-2,3,4,5-tetra-hydrooxepin, i.e. vinylic deprotonation occurs <82JOC3094>. It is of interest that 2,3-dihydrooxepin, like 2,5-dihydrofuran, undergoes allylic deprotonation. The readily available trimethylsilyl ketene acetal of e-caprolactone is a convenient intermediate for the synthesis of 3-RO-substituted e-caprolactones (R is acyl or tosyl) using, as other reagents, lead(IV) carboxylates <83JOC4940> or [hydroxy(tosyloxy)iodo]benzene <89JOC1101>, respectively. 

Furan and Dihydrofuran Synthesis. Trapping the 3-lithio derivative of (1) with decanal leads to the allenic alcohol (eq 2). Aqueous acid under carefully controlled conditions produces 2-trimethylsilyl-5-nonylfuran. The addition product of the 3-lithio... 

Other related reagents are y-butyrolactone, dihydro-5-(hydroxymethyl)-2(3//)-furanone, 2,5-dihydro-2,5-dimethoxy-furan, furan, 5-lithio-2,3-dihydrofuran, and /3-vinyl-a,/3-butenolide. 

So as to confirm whether the cyclopentadiene product was formed from the reaction of aldehydes with di-lithio compounds 1 or with aluminacyclopentadienes 52, in situ NMR experiment was carried out and 52 was observed in the NMR spectrum. Besides, 52 did not react with ketones. However, in contrast, di-lithio reagents could react with ketones to form cyclopentadienes. When 52 was formed at room temperature, no 2,5-dihydrofuran derivatives were generated in the presence of excess aldehydes. Moreover, the reactivity of aluminacyclopentadienes 52 with DMAD was further explored to give benzene derivatives 53 in moderate isolated yields. 

---