Acids Dimethylaluminum chloride

Selective cleavage of THP ethers in the presence of t-butyldimethylsilyl ethers can be accomplished by treatment with mild Lewis acids Dimethylaluminum Chloride (—25 °C to 25 °C, 1 h, 98%) or Methylaluminum Dichloride (-25 °C, 0.5 h, 90%). Selective cleavage of THP ethers of primary, secondary, and tertiary alcohols can be carried out in the presence of t-butyldimethylsilyl, acetyl, mesyl, and methoxymethyl ethers, in the presence of thiostannane catalysts Me2Sn(SMe)2-BF3-Et20 (-20 C or 0 °C, 3-25 h, 80-97%). ... 

Some of the reactions (e.g., that of dimethylaluminum chloride in Table 2) involve redistribution of alkyl and halide groups between the metals. The boronic acids, ArB(OH>2, prepared by Sn/B transmetallation, have been used in Suzuki coupling reactions. It is remarkable that the bistributyltin derivative of 1,1 -binaphthyl undergoes... 

We note that while tin reagents have often been employed for the organoboron halides/ the use of organostannanes as starting materials can also be applied to the synthesis of heavier group 13 derivatives. In the context of polyfunc-tional Lewis acid chemistry, this type of reaction has been employed for the preparation of ort/ o-phenylene aluminum derivatives. Thus, the reaction of 1,2-bis(trimethylstannyl)benzene 7 with dimethylaluminum chloride, methylaluminum dichloride or aluminum trichloride affords l,2-bis(dimethylaluminum)phenylene 37, l,2-bis(chloro(methyl)aluminum)phenylene 38 and 1,2-bis(dichloroalumi-num)phenylene 39, respectively (Scheme 16). Unfortunately, these compounds could not be crystallized and their identities have been inferred from NMR data only. In the case of 39, the aluminum derivative could not be separated from trimethyltin chloride with which it reportedly forms a polymeric ion pair consisting of trimethylstannyl cations and bis(trichloroaluminate) anions 40. 

Ene reaction of aldehydes. Aliphatic and aromatic aldehydes are not reactive enophiles however, in the presence of dimethylaluminum chloride, which serves as u mild Lewis acid catalyst and proton scavenger, ene reactions occur in reasonable to high yield. Use of C2HSA1C1 results in complex mixtures of products. This ene reaction is a useful route to homoallylic alcohols.2... 

Because of the expense of obtaining the Tebbe reagent in its pure form,11 an in situ method for its preparation and use was developed.12 The presence of the excess Lewis acidic by-product, dimethylaluminum chloride, in the in situ preparation may cause reactivity at other sites in the substrate or lower yields of desired products (e.g., 70% vs. 94% for Preparation A, and 65% vs. 85% for Preparation B).Sb However the overall simplicity of the method can be advantageous with readily obtained substrates. 

Prins reaction (cf 10, 186-187). Dimethylaluminum chloride is an effective catalyst for the ene addition of formaldehyde (as trioxane or paraformaldehyde) to mono- and 1,2-disubstituted alkenes.5 When 1.5-2.0 equiv. of the Lewis acid is used, homoallylic alcohols are obtained, usually in high yield. y-Chloro alcohols, formed by cis-addition of -Cl and -CH2OH to the double bond, are sometimes also observed when only 1 equiv. of the Lewis acid is present. The advantage of this reaction over the Prins reaction (using HC1) is that m-dioxanes are not formed as by-products, because formaldehyde no longer functions as a nucleophile when complexed to the Lewis acid. 

This reaction is reversible and suitable p-hydroxy alkenes can be cleaved by heat (17-32). There is evidence that the cleavage reaction occurs by a cychc mechanism (p. 1551), and, by the principle of microscopic reversibility, the addition mechanism should be cyclic too. Note that this reaction is an oxygen analog of the ene synthesis (15-23). This reaction can also be done with unactivated aldehydes and ketones " if Lewis-acid catalysts such as dimethylaluminum chloride (Me2AlCl) or ethyMuminum dichloride (EtAlCl2) are used. Lewis acid catalysts... 

These arrangements are presumably controlled in part by the intramolecular nature of the proton transfer stage of the reaction. While the same stereochemistry is obtained with a variety of Lewis acids, e.g., dimethylaluminum chloride, boron trifluoride-diethyl ether complex, tin(IV) chloride, the opposite preference is observed with bis[4-bromo-2,6-di-/m-buty]phen-oxy](methyl)aluminum (MABR)104 (see Table 6, entries 4-7 and the following example). 

On the other hand, the Diels-Alder reaction of dienes 265 with oximinosulfonates 266 (derived from Meldrum s acid) in the presence of dimethylaluminum chloride afforded the cycloaddition adduct, which was then reacted with alkoxide and oxidizing agent (NCS) to give the desired pyridines 267. ... 

DMAA. See Cacodylic acid DMAA. See N,N-Diethyl acrylamide DMAS. See Dimethylamine borane 4-Dimethylaminobenzene DMAC. See Dimethylaluminum chloride Dimethyl acetamide DMAE. See Dimethylethanolamine DMAEMA. See Dimethylaminoethyl methacrylate... 

Thus, carbonyl ene reactions can be used to prepare cyclic alcohols with an exo-cyclic double bond in 3-position (Scheme 3.78). To gain stereocontrol with respect to an on-ring methyl group, the Lewis acid catalyst is of predominant importance [127]. Therefore, the action of relatively small aluminum species such as dimethylaluminum chloride on ene-aldehyde 403 leads to cis-cyclohexanol 406 with dr 9 1. If, however, the bulky MABR is used, the trans-isomer 407 is formed with dr 32 1. This reversal of stereoselection may be attributed to an equilibrium of adducts 408 and 409. For small Lewis acids, the tendency of the methyl substituent to adopt an equatorial position prevails and 406 is generated. For an increasing bulk of the Lewis acid, the repulsion between the methyl group and the Lewis acid enforces conformer 409 and hence formation of the trans-cyclohexanol 407. 

Using 1 equivalent aluminum Lewis acid (14) derived from (R)-l,l -bi-2-naphthol ((R) BINOL) and dimethylaluminum chloride, reaction of N,N-dimethy-laniline with 2-pyridinecarboxaldehyde in dichloromethane at 20 afforded the para- substituted alcohol in 63% yield with 43% ee as shown in Scheme 6.16. 

Methylseleno esters are readily available in excellent yields by the reaction of Dimethylaluminum Methylselenolate with O-alkyl esters. These selenoesters will acylate reactive arenes (eq 69) and heterocyclic compounds (eq 70) when activated by CuOTf, a selenophilic Lewis acid. Of the potential activating metal salts tested, (CuOTf)2 QHe is uniquely effective. Mer-cury(ll) or copper(l) trifluoroacetates that are partially organic-soluble, as well as the corresponding chlorides, silver nitrate, and... 

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