Alkoxy function

Very stable carbocation (stabilized by both alkoxy function and aromaticity)... 

An excellent route to cyclohexylamines is by hydrogenation of the corresponding aniline over rhodium or ruthenium (17,18,19 2 36,63,64). Rhodium has proved especially useful in saturation of alkoxyanilines with minimal hydrogenolysis of the alkoxy function (45), The extent of hydrogenol ysis occurring in saturation of alkoxyanilines depends also on the solvent. Hydrogenolysis of p-methoxyaniline over Ru(OH)2 fell with alcohol solvent in the order methanol (35%) > ethanol (30%) > propanol (26%) > butanol (22%) > isopropanol (16%) > r-butanol (8%) (43). 

The extent of diastereoselectivity observed in the reaction of l-(l-phenylalkoxy)buta-1,3-dienes with indantrione and alloxane is associated with the steric requirements of the alkoxy function in the chiral auxiliary <96SYN105>. 

Both the regiochemistry and stereochemistry of Wacker oxidation can be influenced by substituents that engage in chelation with Pd. Whereas a single y-alkoxy function leads to a mixture of aldehyde and ketone, more highly oxygenated systems such as the acetonide or carbonate of the diol 1 lead to dominant aldehyde formation.107 The diol itself gives only ketone, which perhaps indicates that steric factors are also important. 

The products are triazolines with the amino or alkoxy function in the 5-position Addition is regiospecific. In some cases the triazolines aromatize spontaneously more usually, aromatization is effected by heating the compounds alone (for enol ether adducts) or with acid or base. 

To improve the levels of selectivity in additions to chiral aldehydes, it is possible to resort to the tactic of double diastereoselection with the use of chiral allylic boranes and boronates (see section Double Diastereoselection ). Bis(isopinocampheyl) allylic boranes and the tartrate allylic boronates (see following section), in particular, are very useful in the synthesis of polypropionate natmal products by reaction with a-methyl and a-alkoxy functionalized aldehydes. 

Oxidation of aromatic alkyl groups. Aromatic methyl or ethyl groups para or ortho2 to an alkoxy function can be oxidized by DDQ in refluxing methanol to aldehydes or methyl ketones, respectively. Simultaneous dehydrogenation can also be effected. ... 

Diastereoselective epoxidation of an allylic alcohol. Epoxidation of either a cis-or Irons-allylic alcohol substituted in the y-position by an alkoxy function by either m-ehloroperbenzoic acid or r-butyl hydroperoxide/VO(acac), results mainly in the anti-cpoxide (9, 109). Epoxidation of the allylic alcohol 1 with m-chloroperbenzoic acid conforms to this pattern, but epoxidation with f-butylhydroperoxide and VO(acac)2 mediated by titanium (IV) isopropoxide favors formation of the jyn-epoxide by a (actor of 10 1. The methyl group attached to the double bond is necessary for this unusual syn-selectivity when it is lacking, epoxidation with f-butyl hydroperoxide/ Ti(l V) is anti-sclcctivc, but less so than epoxidation with the peracid.1... 

A formal iron-catalyzed [3 + 2]-cycloaddition of styrene derivatives with benzoqui-none was reported by Itoh s group [96]. The process is believed to proceed via electron-transfer reactions mediated by a proposed Fe3+/Fe2+ couple, which generates a styrene radical cation and a semiquinone. These intermediates undergo stepwise addition to yield the benzofuran product 51 (Scheme 9.38). The reaction seems to be limited to electron-rich alkoxy-functionalized styrenes, as the Fe3+/Fe2+ redox couple is otherwise unable to transfer the electrons from the styrene to the quinone. 

The ring expansion of 1-alkoxy-functionalized cyclohexane carbaldehydes (Scheme 9.42) was investigated by Kuwajima s group with 50mol% of FeCl3 to yield the ring expansion products 53/54 in 89% yield as a 14 1 mixture of constitutional isomers [100]. 

The first silicone surfactants were prepared by reaction of alkoxy-functional silicones with hydroxyl terminated polyethers using the transetherification reaction [7] ... 

The regioselectivity of the 1,3-dipolar cycloadditions of azides to alkenes is usually difficult to predict due to the similar energies for the transition states which involve either the HOMO (dipole) or the LUMO (dipole). The results of a study which utilized 5-alkoxy-3-pyrrolin-2-ones as dipolar-ophiles in reactions with a variety of aryl azides seemed to reflect this problem the results suggested that the low regioselectivity observed was due to the frontier molecular orbital interactions between dipole and dipolarophile, and not any steric hindrance offered by the 5-alkoxy function <84H(22)2363>. 

AF878) unless in competition with chloro (62YZ584). This must be a direct consequence of steric hindrance by the alkoxy function. Dipole moment measurements show that the groups are in a cis orientation, which hinders oxidation at N-2. Even so, it did prove possible to oxidize some 3,6-dialkoxypyridazines, but not the di-t-butoxy and dibenzyloxy derivatives (55YZ966 66YZ314). 

Aryl substitution produces a bathochromic shift on 1,4-pentadienes so that standard reaction conditions (in solution at X > 250 nm) can be applied. The reaction of equation (4) shows one of the latest examples aimed at understanding the effect of an hydroxy or alkoxy function at the 3-position on the photorearrangement.In the case of the free hydroxy group, two secondary photoproducts were observed besides the two expected vinylcyclopropanes. At variance with this observation, no secondary photoproducts were detected for the phenyldimethylsilyloxy substituent. Direct or benzophenone-sen-sitized irradiation did not cause significant variation in the reaction products. 

A preparation of y-oxygenated allyhc stannanes in which the chirality resides in the alkoxy function has been described (Eq. 41) [61]. The starting alcohol is derived from tri-O-acetyl D-glucal. Acid-catalyzed addition of (Z)-l-methoxy-3-tributylstannyl-l-propene afforded the mixed acetal which was converted to the (Z) enol ether with TMSI and hexamethyldisilazane (HMDS). 

Z)-alkene (79) without loss of the alkoxy functional groups (equation 29). The mechanism of the zinc reduction of alkynes does not appear to have been studied in detail and the factors leading to the observed chemoselectivity and stereoselectivity are not readily apparent. 

A / -elimination reaction also occurs with linear and cyclic glycol mono-alkyl ether radicals. In this case the nucleofugal leaving group is the alkoxy function, RO, as shown in Scheme 7 for base catalysis and a cyclic system in which alkoxide elimination leads to ring-opening [63] ... 

The reciprocal [67] mechanism for ring-opening is H+-catalysis, in which the oxygen at is protonated, resulting in enhancement in the nucleofugal leaving-group properties of the alkoxy function, e.g. 

The silicone reactive functions of alkoxy functional silanes form silanols in the presence of water (Eq. 1). The silane triols formed are very reactive and will react very quickly if other hydroxyl groups are present. For example, they will condense or crosslink with other silanols or with the surface of minerals. The hydrophilic character of the silanols will be lost after the reaction has taken place. 

The absolute configuration of the major products (213) or (214) can be predicted by the chelation model shown in Scheme 40, as the resident stereogenic substituent controls the facial selectivity in the organometallic additions. The diastereoselectivity is affected by the 3-alkoxy functionality. The methoxy substituent is preferred, as the selectivity erodes with benzyloxy substitution (entries 1 and 2, Table 16) and is reversed with the bulky f-butyldimethylsiloxy group (entries 6 and 7, Table 16). As expected, selectivity is poor for nitrones devoid of (3-alkoxy substituents (entry 3, Table 16). By appropriate nitrone/organometallic substitution, both diastereomeric products can be preferentially generated (entries 1 and 6, Table 16). 

Regarding this development, it is surprising that so far only one y-alkoxy-functionalized propyltriethoxysilane ((3-ethoxypropyl)triethoxysilane) has been described in the chemical literature [4, 5]. It was prepared from sodium ethoxide and (3-chloropropyl)triethoxysilane in an ether synthesis according to Williamson. This procedure is not suited for the synthesis of other alkoxypropyltriethoxysilanes because of the possible exchange of alkoxy groups [6],... 

Stabilizing the vanadium with auxiliary ligands makes it possible to form complexes with various functionalities including the alkoxy functionality. Such classes of ligands include pyrazolyl borates (15)102 and Schiff bases, and will be described in the appropriate multidentate ligand section. 

The alkoxy-functionalized silylene-bridged ansa-Qp-Flu zirconocene dichlorides bearing a 6-/[Pg.959]

A new class of compounds, macrocyclic polyethylenoxysilanes, called silacrowns have been prepared which demonstrate phase transfer catalytic properties. An alkoxy functional silacrown has been immobilized in a single-step reaction on a siliceous support. The immobilized silacrown also demonstrates phase transfer catalytic properties. A functionalized onium phase transfer catalyst was also prepared that reacts directly with a siliceous support and is catalytically active. 

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