Isopropylidene methyl group

The initial hydroxylation in the degradation of some terpenes the ring methylene group of camphor by Pseudomonas putida (Katagiri et al. 1968 Tyson et al. 1972 Koga et al. 1986), and the isopropylidene methyl group of linalool by a strain of P. putida (Ullah et al. 1990). 

The fact that in 64a the monodentate ligands are cis to each other, as has been found in numerous other hexacoordinate bis-acylimidato-7V,(9 chelates 30-38,43-50 suggests that in the absence of special constraints the cis orientation is preferred. It follows that the uncommon trans geometry, found in 65 and 66, is the result of steric repulsion between the bulkier Si-Cl and Si-Br bonds and the isopropylidene methyl group. All three dihalo-complexes (the cis-64 and trans-65 and 66) react readily with... 

In this section, we have made an attempt at selectivity, in view of the very large amount of literature produced as a result of the commercial interest in chrysanthemic acid and the pyrethroids. In addition to a review in Japanese of the synthesis and reactions of chrysanthemic acid, there is an excellent review of the pyrethroid acids with an exhaustive literature list up to 1980. We shall only try to complete the latter. Many syntheses are destined as general routes for the preparation of substituted chrysanthemic acids, and those in which the isopropylidene methyl groups are replaced by halogen atoms. 

Table 2. Chemical shifts 8 (ppm) of isopropylidene methyl groups of 5,14, and 19 in CDCI3 (100 MHz).

The observed exclusive cis fusion and the predominance of the product 355 over 356 was ascribed to the reaction occurring via the preferred transition state 354, wherein steric repulsion between one of the methyl groups of the dioxolane ring and the methylene group f) to nitrogen is minimised. Final introduction of one carbon atom to achieve the crinane skeleton was accomplished with Eschenmoser salt. The product, the O-isopropylidene derivative of the alkaloid, on acid catalysed deketalisation furnished (-)-amabiline with an impressive overall yield of 43%. 

By combining all the results, a comprehensive picture of the motions occurring in bulk BPA-PC is reached. At very low temperatures, the first motions to occur are the rotations of the methyl groups of the isopropylidene unit around the C3 axis. The activation energy associated with this y transition is around 8 kj mol-1. 

Indeed, stereospecific 1,4-additon of methyl lithium/copper iodide to the conjugated system of the above enone was initially reported by the authors(3 // We synthesized this convenient synthon and attempted to functionalize it further by removal of isopropylidene protecting group followed by acetylation at C-2. (scheme 13). All attempts failed due to extensive decomposition of the starting material, presumably through the p-elimination with formation of secondary polymerization products. 

Ohle and Just112 have carried out the following sequence 1,2-isopro-pylidene-D-fructopyranose 3-p-toluenesulfonate —> l,2-isopvopylidene-3,4-anhydro-D-psicose —> l,2-isopropylidene-4-methyl-D-sorbose (VII), ([a]D -81.6°). Since the introduction of a methyl group does not alter greatly the specific rotation, it is to be expected that the parent 1,2-iso-... 

The X-ray structure of two isomers of fulgide 35 have been determined by Yoshioka et al.56 In the E form, the succinic anhydride and the furyl ring were not coplanar and were considerably twisted relative to each other. This is due to the steric hindrance effect between the isopropylidene group and the 2-methyl group in the furyl moiety. The distance between the two reactive sites, which corresponds to the chemical bond formed during photocyclization, was 3.44 A. 

---