Ring inserts

The reaction of l,4-bis(trimethylsilyl)-l,3-butadiyne (174) with disilanes, followed by treatment with methylmagnesium bromide, produces i,l,4,4-tetra(-trimethylsilyl)-l,2,3-butatriene (175) as a major product[96]. The reaction of octaethyltetrasilylane (176) with DMAD proceeds by ring insertion to give the six-membered ring compounds 177 and 178[97], The l-sila-4-stannacyclohexa-2,5-diene 181 was obtained by a two-step reaction of two alkynes with the disilanylstannane 179 via the l-sila-2-stannacyclobutane 180[98],... 

Methyl polyfluoro-1-cyclobutenyl ethers react with sulfur trioxide to form fluoride and polyfluorocyclobutenones, but coproducts are their fluorosulfonyloxy derivatives resulting from sulfur trioxide insertion [5] (equation 5) The nonsul-fonyloxylated polyfluorocyclopentenones are favored when starting with methyl polyfluoro-1-cyclopentenyl ethers (equation 6). Ring insertion of sulfur tnoxide occurs during the reaction of 1-methoxytnfluorocyclopropene (equation 7)... 

In the case of the oxiranes, the insertion is promoted by the strain of the three-membered ring. Insertion of the metal atom produces a surface-adsorbed four-membered metallaoxacyclobutane, and this process decreases the ring strain. 

Figure 19. Packing arrangement of sucrose delineated by the observed crystal faces, as viewed along the c axis. The emerging galactose moiety of a raffinose inhibitor molecule has been inserted at the (110) face in the exo conformation. Note that the corresponding hydroxyl of sucrose adopts an endo conformation. The sugar ring inserted at the (lTO) face indicates the position that would be taken by the galactose moiety of a raffinose inhibitor molecule in the endo conformation.

R. Grubbs, C. Bielawski, and D. Benitez, Synthesis of macrocyclic polymers by ring insertion polymerization of cyclic olefin monomers, US Patent 6946533, assigned to California Institute of Technology (Pasadena, CA), September 20,2005. 

Ring Opening and Ring Insertion of Silacyclobutanes and Germacyclobutanes 592... 

Intramolecular dehydrocondensation of the /3 -germylethanethiol (65) gives the 2-germathietane, which decomposes by /3-elimination. The germathione intermediate then ring inserts into the germathietane (Scheme 98) (80MI12000). 

The net effect of this cyclohexadiene/phenyl ring insertion at the carbonyl group is to cause an increase in the overall equilibrium constant for the addition of solvent water, from A dd = 2.3 x 103 for hydration of formaldehyde154 to A dd = 4.0 x 107 for hydration of the p-quinone methide l,3 so that Kj = AT. dd/Aiadd = 1.7 x 104 for transfer of the elements of water from formaldehyde hydrate to 1 (Scheme 43). We have proposed that the relatively small driving force of 6 kcal/mol for this transfer of water from CH2(OH)2 to 1 represents the balance between larger opposing effects3 ... 

When only 0.1 equiv of triethylamine was used, 3-(chlorosilyl)propyl ketone was formed as the major product in 86% estimated yield (based on NMR analysis). According to the authors mechanistic hypothesis, oxidative insertion of the transition metal catalyst occurs into the acid chloride, which is followed by ring insertion of the acylpalladium... 

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