Tetra-Substituted Alkenes

Meyers, A.I., Heterocycles in Organic Synthesis John Wiley Sons, Inc., New York, NY., pp. 285-286 (1974). 

Yamamoto, Y., Wojcicki, A Inorg. Nucl. Chem. Lett., 8,833 (1972) JCS Chem. Comm., Q%Z 912), Inorganic Chem., 1779(1973). 

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Acetylene- and Diacetylene-Expanded Cycloalkanes and Rotanes. 201 1 -42 de Meijere A, Kozhushkov SI, Khlebnikov AF (2000) Bicyclopropylidene - A Unique Tetra-substituted Alkene and a Versatile Cj-Building Block. 207 89-147 de Meijere A, Kozhushkov SI, Hadjiaraoglou LP (2000) Alkyl 2-Chloro-2-cyclopropylidene-acetates - Remarkably Versatile Building Blocks for Organic Synthesis. 207 149-227 Dennig J (2003) Gene Transfer in Eukaryotic Cells Using Activated Dendrimers. 228 227-236 de Raadt A, Fechter MH (2001) Miscellaneous. 215 327-345 Desreux JF, see Jacques V (2002) 221 123-164... 

Thus, Alami and coworkers [102] have shown that benzylhalides as 6/1-201 can react with 1-alkynes as 6/1-202 in the presence of Pd° and Cul in a Sonogashira reaction which is followed by a Heck and a second Sonogashira reaction to give tetra-substituted alkenes 6/1-203 in yields of 22 to 90% (Scheme 6/1.52). 

For tetra-substituted alkenes [107], it was necessary to rely on the more reactive cationic Zr equivalent generated from [(EBTHI)ZrMe2] and either methyla-luminoxane or [PhMe2NH]+[Co(C2B9H11)2] developed earlier by Waymouth et al. [104]. Using H2 pressure ranging between 5 and 133 bar, it was possible to obtain the hydrogenated products with 80-98% ee in most cases (Table 6.3). 

Table 6.3 Enantioselective hydrogenation of tetra-substituted alkenes catalyzed by [(S,S)-(EBTHI)ZrMe2]/[PhMe2NH+B(C6F5)4V)...

Ionic hydrogenations of C=C bonds generally work well only in cases where a tertiary or aryl-substituted carbenium ion can be formed through protonation of the C=C bond. Alkenes that give a tertiary carbenium ion upon protonation include 1,1-disubstituted, tri-substituted and tetra-substituted alkenes, and each of these are usually hydrogenated by ionic hydrogenation methods in high yields. 

FIGURE 3-23 Hydrocarbons in gasolines (G). automobile exhaust (E), and ambient urban air (A). A, A, A, A mono-, di-, tri-, and tetra-substituted alkenes. X not found. Hatching > not found in California. 

The cycloaddition of substituted acrylates has been investigated with cyclic nitronate 24 (Table 2.49) (14). The cycloaddition of a 1,1-disubstituted dipolar-ophile (entry 2), proceeds in good yield, but both 1,2-disubstituted alkenes fail to react. The effect of substitution pattern on the dipolarophile was investigated with a slightly more reactive nitronate (Table 2.50) (228). Less sterically demanding alkenes such as cyclohexene, cyclopentene, and methyl substituted styrenes react, albeit at elevated temperature. The only exception is the 1,1-disubstituted alkene (entry 4), which reacts at room temperature. Both stilbene and dimethyl fumarate fail to provide the desired cycloadduct. In a rare example of the dipolar cycloaddition of tetra-substituted alkenes, tetramethylethylene reacts at 50 °C over 3 days to give a small amount of the cycloadduct (entry 7). 

The conjugate addition of organocopper reagents to ot,(3-alkynic esters, ketones, aldehydes and acids is a useful method for the preparation of various tri- and tetra-substituted alkenes,87 although addition to aldehydes is less common.88 Use of a vinylcuprate results in the formation of a conjugated dienone, which further highlights the importance of this methodology (equation 43 ).87... 

Use of a-oxoketene dithioacetals and organocuprates provided a stereoselective synthesis of tri- and tetra-substituted alkenes.109 In fact, it was reported that either the (E)- or (Z)-alkene could be prepared by the proper choice of cuprate and of the sequence of addition (Scheme 21). 

The addition of aryl halides and divinyl or enyne carbinols to give tri- or tetra-substituted alkenes is considered to involve skeletal reorganization (Scheme 89) of an intermediate cyclopropanol.132 The ability to suppress /3-hydride elimination of organopalladium intermediates is critical to the success of these processes. 

Remarkable regioselectivity was observed in the thermal migration of the tetra-substituted alkene Z-83. Hydroboration of this compound furnishes only the migration product in the direction of the ethyl group. Furthermore, the migration was stereoselective providing, after the standard amination sequence, the benzylic amine 85 in 46% yield. The diastereoselectivity was 95 5 between C(l) and C(2) and >99 1 between C(2) and C(3) (Scheme 17) [7, 8, 13],... 

The tertiary cation can lose a proton in either of two positions. One of the products (B) is a tetra-substituted alkene, and the other (C) is disubstituted. 

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