2- -2-propenyl methyl

Stereochemical integrity may also be lost when the reaction of a stereoisomer occurs via an intermediate which retains a stereogenic element, but whose bonding permits interconversion of stereoisomers faster than its conversion of stereoisomeric products. [2 + 21-Cycloaddition of TCNE and cis-propenyl methyl ether [30] yields cis- and trans-adducts, 22 in Scheme 9.13, in ratios which depend on the solvent (84 16 in favour of the cis-adduct in acetonitrile). The dipolar 23 was proposed as an intermediate. The initial bonding destroys the double bond character between Cl and C2 of the enol ether reactant, and the much... 

Scheme 9.13 Loss of stereochemical integrity in cyclobutane formation from TCNE and c/s-propenyl methyl ether.

A thorough stereochemical study of a very similar reaction with cis- and trunj-propenyl methyl ether as electron-rich alkenes provides comparable findings. The trans isomer of 1,2-bis(trifluoromethyl)-l,2-dicyanoethylene and cis-propenyl methyl ether (112) gave adducts (113), (114) and (115). In some cases, adducts revealing some loss of stereochemistry in the enol ether component were detected and identified. 

The spectral series depicted in Fig. 4.18(a) were measured during the hetero-Diels-Alder reaction of the phthalimidobutenone 1 with propenyl methyl ether 2 to yield the diastereomeric dihydropyrans 3 and 4. The transformation is monitored via the carbonyl modes of the phthalimido moiety. It should be noted, however, that the two diastereomers, 3 and 4, cannot be distinguished by the i.r. absorption of these vibrations. The reaction in Scheme... 

Benzyne, when added to the geometric isomers of propenyl methyl ether (in dichloromethane at 40°C) gives mixtures of 1,2-adducts, approaching within 65% of the equilibrium composition . Non-stereospecific 1,2-cycloadditions of benzyne to cis and trans isomers of 1,2-dichloroethylene and propenyl ethyl ether have also been reported in both cases the products are far from completely equilibrated, indicating a stepwise addition with a relatively fast ring closure . 

An alternative route starts from furan (19). Reaction with bromine in methanol leads to 2,5-dimethoxy-2,5-dihydrofuran (20) which is transformed to but-2-ene-1,4-dial bisdimethyl-acetal (21). Double enol ether condensation with 1-propenyl methyl ether (22), followed by acetal hydrolysis and elimination, provides crystalline (all- -Cio-dialdehyde 8 in an overall yield >50% [13]. 

The Ci3-ketone /-ionone (2) is built up in five stages (5 + 4—from the starting materials acetone (3) and acetylene (4), with sigmatropic rearrangements playing a key role (Scheme 1). The process comprises four basic reactions, ethynylation, partial hydrogenation, reaction with wo-propenyl methyl ether (9) and rearrangement, which can be carried out inexpensively [11]. 

Alternatively, furan may also be brominated and then subjected to an exhaustive methanolysis. A zinc chloride-catalysed double enol ether condensation with 1-propenyl methyl ether (Miiller-Cunradi-Pieroh reaction) gives finally the crystaUine (aU )-Cio-dialdehyde in an overall yield of >50 %. 

When onion is cut or cmshed, ( )-5 -l-propenyl-L-cysteine sulfoxide (isoalliin) is converted into ( )-l-propene-l-sulfenic acid. Different from garlic, (Z)-thiopropanal S-oxide, a lachrymatory factor, is formed from the sulfenic acid by lachrymatory factor synthase (Figure 18.6). The remaining ( )-l-propene-l-sulfenic acid and methyl sulfenic acid produced from 5 -methyl-L-eysteine sulfoxide ean form methyl 1-pro-pene-thiosulfinate and 1-propenyl methane thiosulfinate that are further converted to sulfides such as 1-propenyl methyl disulfide and 1-prope-nyl methyl trisulfide. 

Singlet oxygen reacts with olefins presumably by the "ene" reaction to form allyflc hydroperoxides (45,57), eg, l-methyl-2-propenyl hydroperoxide [20733-08-8] is produced from 2-butene (eq. 19). The regioselectivity of this reaction has been investigated (58). 

Purine, 9-methyl-8-thioxo-7,8-dihydro-synthesis, 5, 578 Purine, 2-oxo-synthesis, 5, 587 UV spectra, 5, 517 Purine, 8-oxo-synthesis, 5, 576 UV spectra, 5, 517 Purine, 2-oxodihydro-alkylation, 5, 532 Purine, 2-oxo-2,3-dihydro-synthesis, 5, 596 Purine, 8-oxo-7,8-dihydro-synthesis, 5, 577, 582, 596 Purine, 6-oxo-2-thioxo-synthesis, 5, 574 Purine, 6-oxo-8-thioxo-synthesis, 5, 578 Purine, 6-phenacylthio-nucleosides dethiation, 5, 558 Purine, 8-phenyl-synthesis, 5, 575, 576 Purine, 8-phenyloxo-synthesis, 5, 576 Purine, 9-phenyl-8-thioxo-synthesis, 5, 578 Purine, 9-(2-propenyl)-synthesis, 5, 592 Purine, 8-(2-pyridyl)-synthesis, 5, 576 Purine, 8-(3-pyridyl)-synthesis, 5, 576... 

Pyran-2-one, 4-methoxy-6-( 1 -propenyl)-synthesis, 3, 690 Pyran-2-one, 6-methyl-bromination, 3, 690 Pyran-2-one, 6-(2-methylpropenyl)-synthesis, 3, 796 Pyran-2-one, 3-methylthio-synthesis, 3, 796 Pyran-2-one, 3-nitro-6-phenyl-oxidation, 3, 681 Pyran-2-one, 6-phenyl-chlorination, 3, 679... 

Vinyl Inflates permit alkylation with vinyl cations [24, 25] Fluorobenzene reacts with 2 methyl 1-phenyl 1 propenyl triflate to form a diaryl alkene [24J (equation 17)... 

It is noteworthy that the kinetics indirectly provided the evaluation of the basicities of these enamines [Eq. (4)]. The pK values for 4-(2-methyl-propenyl)morpholinc, l-(2-methylpropenyl)piperidine, and l-(2-methyl-propenyl)pyrrolidine are 5.47, 8.35, and 8.84, respectively (27). Since the protonation of the j8-carbon atom does not possess the character of a real equilibrium at pH 7 and up [for compound 1 even at pH 1 and up] the basicity must be fully ascribed to the equilibrium between enamine and the corresponding nitrogen-protonated conjugate acid. 

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