1 -alkoxy- l-

Incomplete simple diastereoselectivity. combined in at least some cases with lower induced stereoselectivity, is also found in the addition of silylketene acetals 1-alkoxy-l-trirnethylsilyloxy-l-propene to 2-benzyloxypropanal3. On the other hand, a single diastereomeric adduct results from the tin(IV) chloride mediated addition of the following enolsilane to (S )-2-benzyloxypropanal12. 

Burkhouse, D. and Zimmer, H., Novel synthesis of 1-alkoxy-l-arylmethane-phosphonic acid esters, Synthesis, 330, 1984. 

A related method was reported by Katritzky et al. [25], who prepared 1-alkoxy-l-(l,2,4-triazol-l-yl)allenes from the corresponding triazole-substituted alkynes, e.g. the reaction of 18 to 19 in Eq. 8.2. In this case the generated allenyl anion was trapped with methyl iodide. 

An exceptional approach to phosphorus-substituted alkoxyallenes via isomerization of alkynes was introduced by Beletskaya s group. The treatment of 1-alkoxy-l-propynes 23 with l-halo-2,2-bis(trimethylsilyl)phosphaethen 24 furnished alkoxyallenes 25 (Scheme 8.9) [31]. 

Pericas and coworkers173 studied the endo selective reactions of 1-alkoxy-l,3-butadienes and 1-alkoxy-l,3-octadienes with maleic anhydride. They found that the trans-2-phenyl-cyclohexan-l-ol and 3-exo-(neopentyloxy)isobornan-l-ol based chiral dienes induced the highest facial selectivities. The relative transition state energies for the formation of the different diastereomers were calculated using semi-empirical methods (AMI). 

Binaphthol catalyst 417 proved effective in the cycloadditions of 1-alkoxy-l,3-butadienes with methacrolein and 1,4-naphthoquinone257. More recently, it was found that the use of molecular sieves was essential for the in situ preparation of the catalyst, but also that this had dramatic effects on the enantioselectivity258. In the presence of molecular sieves, the cycloaddition of juglone (342) with 1-acetoxy-l,3-butadiene was catalyzed by 10 mol% of 417 to give cycloadduct 343 with only 9% ee. In the absence of molecular sieves, the enantiomeric excess increased to 76-96% (equation 124). 

For example, Nakamura and Kuwajima [15] have described 1-alkoxy-l-trimethylsilyloxycyclopropanes (15) -prepared by reductive silylation of alkoxy 3-chloropropanoates-, which react with aliphatic aldehydes, but not with ketones, in the presence of one equivalent of TiCl4 to give good yields of y-lactones 17 through the acyclic derivative ethyl 4-hydroxybutanoate (16) (Scheme 5.10). With aromatic aldehydes and their acetals the reaction leads directly to acyclic 1,4-D derivatives. 

Unlike their enolate counterparts, homoenolates have been underrated because of a prior lack of synthetic accessibility. Many of the previously known homoenolates cyclize readily to the cyclopropanolate tautomer and behave chemically as the latter. 1-Alkoxy-l-silyloxycyclopropanes have provided,... 

Pr, or Bu),88 alkyl-substituted 1-alkoxy-l,3-butadienes (for example, 202) were also used.89-91... 

Attempts were made in order to obtain adducts 198 in enantiomeric form by cyclo-addition of 1-alkoxy-l,3-butadienes to optically active esters of glyoxylic acid96 the enantiomeric purities of the adducts were, however, poor.96 Optically active butyl 2-alkoxy-5,6-dihydro-2H-pyran-6-carboxylates (198, R1 = Bu) were obtained when the R group in 197 was a carbohydrate moiety. The diastereoisomers resulting from cyclo-addition were separated by chromatography (see Section VII and Ref. 350). 

As mentioned on p. 60, 1 -1-dihydroxy-X -phosphorins 90a (R=H) exist almost entirely in the 2-hydro-phosphinic acid form 90b. The same holds for the 1-alkoxy-l-hydroxy-X -phosphorins (R = alkyl). 

In 1977, an article from the authors laboratories [9] reported an TiCV mediated coupling reaction of 1-alkoxy-l-siloxy-cyclopropane with aldehydes (Scheme 1), in which the intermediate formation of a titanium homoenolate (path b) was postulated instead of a then-more-likely Friedel-Crafts-like mechanism (path a). This finding some years later led to the isolation of the first stable metal homoenolate [10] that exhibits considerable nucleophilic reactivity toward (external) electrophiles. Although the metal-carbon bond in this titanium complex is essentially covalent, such titanium species underwent ready nucleophilic addition onto carbonyl compounds to give 4-hydroxy esters in good yield. Since then a number of characterizable metal homoenolates have been prepared from siloxycyclopropanes [11], The repertoire of metal homoenolate reactions now covers most of the standard reaction types ranging from simple... 

The common Lewis acids in this group, A1C13 and BX3, do not form metal homoenolates in their reaction with siloxycyclopropanes, only GaCl3 reacts with 1-alkoxy-l-siloxycyclopropanes 1 to give propionate homoenolates [11]. 

There are a few points to be addressed in order to understand the mechanism of homoenolate formation. Several lines of experimental evidence for the reaction of 1-alkoxy-l-siloxycyclopropanes have provided insights into the nature of the metal interacting with the siloxycyclopropane. 

I. From Aldehydes and Ketones with 1-Alkoxy-l-lithiocyclopropanes and from Enol Ethers by Cyclopropanation... 

Thus, strong shieldings are observed for fi carbons of enol ethers and alkynyl ethers, as shown for 1,1 -dimethoxyethene (54.7 ppm) and ethoxyethyne (23.4 ppm) in Table 4.26. In 1-alkoxy-l,3-butadienes, transmission of the electron releasing effect along the conjugated double bonds affects alternate carbons similarly, shielding the carbons in / and <5 position as illustrated for l-ethoxy-2-methyl-l,3-butadiene. 

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