Ethylenes trisubstituted

M. St. C. Flett and P. H. Plesch, J, Chem. Soc., 1952 3355, found evidence for the presence of the trisubstituted ethylene end group and also for trichloro-acetate end groups in low molecular weight polyisobutylenes prepared at 0°C using TiCh and CI3COOH as catalyst and co-catalyst, respectively. For results on the similar polymerization of styrene with TiCh, see P. H. Plesch, J. Chem. Soc., 1963, 1653, 1659, 1662. 

The chlorodifluoromethylated ketone 130 proved to be a valuable substrate for promoting SrnI subtitution reaction with sodium phenylthiolate and to generate a new a-(phenylthio)-a,a-difluoroacetophenone derivative 131 (Equation 57) <2001TL3459>. Upon treatment with nitronate anions under classical SrnI reaction conditions or MW irradiation, 6-chloromethyl-5-nitro-imidazo[2,l- ]thiazole 132 yielded 5-nitroimidazothiazoles bearing a trisubstituted ethylenic double bond at the 6-position (Equation 58) <2001SC1257>. 

Ethylene and styrene derivatives react with various propargylic silyl ethers in the presence of zirconocene(II) to afford allenic products in high yield (Scheme 5.7). For example, substrate 67 was transformed into the trisubstituted allene hydrocarbon 68 in 93% yield under the reaction conditions [20]. In the synthesis of various tetraalkylated allenes, in which several of the alkyl substituents also contained triple bonds, allowing these substrates to be cydized intramolecularly into aromatic com-... 

This manganese-copper-catalyzed conjugate addition reaction compares favorably with the classical copper-catalyzed reaction. The two reactions are easily and similarly carried out under mild conditions, but the first one gives higher yields. This difference, already observed in the case of p-monosubstituted o,p-ethylenic ketones, is especially noticeable with p,p-disubstituted or [Pg.70]

In the absence of H2 and other transfer agents, polymer molecular weight is limited by various P-hydride transfers—from normal (1,2-) and reverse (2,1-) propagating centers, before and after rearrangement [Lehmus et al., 2000 Resconi et al., 2000 Rossi et al., 1995, 1996 Zhou et al., 2001] (Sec. 8-4i-2). Vinylidene, vinylene, and trisubstituted double-bond end groups are formed in 1-alkene polymerizations, vinyl and vinylene in ethylene polymerization. [Vinyl groups are also produced in some 1-alkene polymerizations, not by P-hydride transfer, but by P-alkyl transfer (Sec. 8-4i-2).]... 

Our work is in fact supported by Tanaka s results who sometimes after us proposed a synthesis of trisubstituted a,6-ethylenic esters from this same molecule (6). 

Fig. 3.44. Stereo- and regioselective formation of a bromohydrin from a trisubstituted ethylene conversion to an epoxide.

The reaction7641 of 2-chloromethyl-5-nitrothiophene with the 2-nitropropane anion was recently reinvestigated, and extended to various nitronate anions76b. These reactions, taking place by the S l mechanism, afforded good yields of new 5-nitrothiophenes bearing a trisubstituted ethylenic double bond at the 2-position. Some of these derivatives showed the same antiprotozoan activity as that of reference compounds. 

Fig. 13.1. Stereoselective synthesis of a trisubstituted ethylene by way of C,C coupling of a Gilman reagent. The Cs ,2-triflate bond is converted into the Csp2—C bond of the product with complete retention of configuration.

Selenophene chloromethyl derivatives readily form di(/3-hydroxy-ethyl)aminomethylselenophenes (8) which, with thionyl chloride, give the corresponding di(/3-chloroethyl)aminomethylselenophenes (9).103 Chloromethylselenophenes condense with trisubstituted ethylene-diamines to yield tetrasubstituted diamines containing the selenophene nucleus.104 The reaction of 2-chloromethylselenophene with sodium derivatives of malonic and acetoacetic ester yields the acid (10) and ketone (11), respectively, whereas with alkyl magnesium halides 2-(alkylmethyl)selenophenes are formed.105... 

In the previous examples, disubstituted double bonds have been synthesized via ring-closing metathesis. As shown in Scheme 5, it is possible to extend the method to tri- or tetrasubstituted double bonds. Thus, bisallylic ether 33 leads to the trisubstituted olefin 34 and compound 35 gives the tetrasubstituted olefin 36 [3]. Here, the additional substituents are simple methyl groups, but silyl groups for example, can be introduced too. The volatile byproducts in these cases are not ethylene but butene or propene. 

The conclusion is supported by vibrational FT-IR and FT-Raman spectra of 33a-g in the neutral and doped state [104,105], A comparison of the intensities of the FT-IR bands from 1,3,5-trisubstituted benzene end group signals near 704 cmwith the intensities of the C-H out of plane motion of l,2-tro s-disubstituted ethylenes near 964 cm shows a linear decrease of the intensity ratios with increasing chainlength approaching very small values for 8-10 units. 

Dibromoborane-dimethyl sulfide exhibits regioselectivity in hydroboration of alkenes which is comparable to that exhibited by dialkylboranes. Excess alkene should be avoided in reactions of trisubstituted ethylenes, otherwise hydrogen bromide liberated during work-up may add to the excess ethylene and cause problems. 

A full report on the c.d. of square-planar complexes formed between chiral olefins and sodium tetrachloroplatinate shows that a quadrant rule (Figure 6) predicts the sign of the Cotton effect near 440 nm for a range of disubstituted and some trisubstituted ethylenes. The Pt atom is considered to bond to the less-hindered face of the olefinic bond. Despite the success of the quadrant rule... 

Reductive cleavage of imidazolidines 641 was implicated in the one-pot synthesis of N,N,N -trisubstituted ethylenediamines 643 from V,V -disubstituted ethylene diamines and an aldehyde R CHO. Presumably the intermediate iminium ion 642 is reduced by NaBH4 (Scheme 154) <2003SC3193>. Naphthalene-catalyzed lithiation of l,3-dimethyl-2-phenylimidazoline 644 leads to benzylic C-N bond cleavage. The intermediate dianion can be trapped with electrophiles (HjO, alkyl halides, ketones, and aldehydes) to afford diamines 645 <2005T3177>. 

The prefixes cis and irons work very well for disubstituted ethylenes and some trisubstituted ethylenes. But how are we to specify configurations like these ... 

---