Via opening

Lewis acid promoted condensation of silyl ketene acetals (ester enolate equiv.) with aldehydes proceeds via "open" transition state to give anti aldols starting from either E- or Z- enolates. 

Due to the nature of batch operations, transferring and charging of process materials is a common activity. This can entail gas, liquids, and/or solids handling via open equipment. This may include pumping of liquids from drums or dumping of solids from other containers into an open vessel, shoveling material into a dryer, or making temporary connections such as at hose stations. 

An interpretation of activation parameters has led to the conclusion that the bromination transition state resembles a three-membered ring, even in the case of alkenes that eventually react via open carbocation intermediates. It was foimd that for cis trans pairs of alkenes tiie difference in enthalpy at the transition state for bromination was greater than the enthalpy difference for the isomeric alkenes, as shown in Fig. 6.2. This... 

Not all cells in the heart express the fast sodium channel. Thus, sinus nodal and atrioventricular nodal cells lack the fast Na+ channel and instead generate their action potentials via opening of Ca2+ channels. This is the basis for their sensitivity to Ca2+ antagonists. 

Metal is then deposited into the opened vias (openings) in the oxide layer and over its surface. During the subsequent photolithography process, it is patterned to form the desired electrical interconnections. These two steps are repeated for each succeeding level to produce additional levels of interconnections. Finally, a protective overcoat of oxide/nitride is applied (passivation), and vias are opened so that the wires eonnectlng the IC chip to its carrier package can be bonded to output pads. 

The latter reacts with a second DMAD molecule to give cycloadduct (726). The reaction proceeds via opening of the aziridine ring to give compound (725). The cyclo-adduct (726) undergoes a 1,3-sigmatropic shift and aromatization to give compound (723) (Scheme 2.302) (816). 

We considered [71] the epoxidation activity of MoVI hydroperoxo intermediates formed via opening an ti2-02 peroxo group ... 

A plausible alternative mechanism involves as a first step the formation of a linear dimer, XB=NR—BX=NR, according to the left part of Eq. (21). This linear dimer will be more stable in entropy but less stable in energy than the corresponding cyclodimer. The second step would be addition of iminoborane to the open-chain dimer giving the borazine in either a concerted or a two-step mechanism. The intramolecular cyclization of the open-chain dimer, according to the right-hand side of Eq. (21), would compete addition of an iminoborane. We cannot definitely exclude a mechanism via open-chain dimers. 

SCHEME 9. Durette, Hough, and Richardson s synthesis of methyl 3-bromo-3-deoxy-p-maltoside via opening of the 2,3-allo-epoxide derived from the l,2,2, 3, 4, 6,6 -heptaacetate of methyl p-maltopyranoside (1974). 

Stereochemically, even more interesting are the bis-l,3-oxathiane derivatives 98 and 99 <2005STC369>. All compounds are chiral and the chiral elements are carbons C-2/C-2 and the 1,3-oxathine moieties themselves (Equation 9). Due to the bis-structure, compounds 98 and 99 exhibit both homochiral iZR,2 R ZS,Z S) and hetero-chiral (2R,Z S) isomers (Scheme 4) and they reveal rapid equilibration in solution via open-chain intermediates, thereby preventing separation and individual analysis of the isomers in solution. In the solid state, the compounds crystallized either as unique heterochiral isomers or as a mixture of the two as a solid solution. 

Regioselectivity was observed when the reaction was extended to the use of substituted hydrazines, where the reaction of 3,4-pyridinedicarboximide derivatives 305 or 306 with methylhydrazine in boiling ethanol gave the corresponding 3-methyl-l,4-dioxo-l,2,3,4-tetrahydropyrido[3,4-r pyridazine 307 and 2-methyl-l,4,5-trioxo-1,2,3,4,5,6-hexahydro analogue 308, respectively, via opening of the imide ring and evolution of ammonia gas... 

Frequently, five-membered heterocyclic systems have provided the C(3)N(4)C(5)C(6) fragment in 1,2,4-triazine syntheses. For instance, the oxazol-5-one (586) reacts with hydrazines to give, via open-chain intermediates (587), the l,2,4-triazine-3,6-diones (588)... 

The [Zn4(SPh)10]2- cluster anion has also been prepared by the reaction of NaSPh with ZnCl2, and H NMR studies have revealed a rapid SPh(bridgmg)-SPh(terminal) interconversion, which is thought to occur via opening of the cluster by successive breaking of two bridging Zn—S bonds.820 A rapid metal exchange reaction in the mixed-metal clusters [M4 Zn (SPh)io]2 (M = Cd, Co or Fe) and [Co4 Cd (SPh)io]2- was also detected. 

The epoxides (11) derived from 2-substituted allylic alcohols (10) are particularly susceptible to nucleophilic attack at C-3, a reaction that is promoted by Ti(lV) species [18]. When stoichiometric amounts of Ti-tartrate complex are used in these epoxidations, considerable product is lost via opening of the epoxide before it can be isolated from the reaction. 

Ingold3 has used the term SE2 to describe these bimolecular substitutions which proceed via open transition states (as shown in reaction (4)), but Reutov4 uses the symbol SE2 to describe all bimolecular electrophilic substitutions, including those in which cyclic transition states are formed as well as those in which the transition state is open. More recently, Abraham et at.6 have suggested that bimolecular electrophilic substitutions in which an open transition state is formed could more explicitly be denoted by the term SE2(open). 

Interestingly, the use of optically active alcohol 51 in this protocol leads, after cleavage of the benzylic ether in the initial adduct 52, to the enantiomerically enriched homoallylic alcohol 26. This approach appears to be the first asymmetric preparation of homoallylic alcohols via open-chain acetal derivatives (Scheme 13.19). 

Scheme 9 Another mechanism via open-chain intermediate...

Sending photons via open air requires identifying QKD photons from others such as coming from the sun. In the NIST system QKD photons are time stamped and looked for only when they are expected to arrive. 

Figure 3 shows five possible paths, designated a e, generating r 2-H2 complexes from 1 via open site intermediates. Note that paths a-d, leading from 1 to species 7 10, are all overall endothermic processes. Paths a-c can be resolved into the endothermic creation of the open site, followed by the exothermic coordination of dihydrogen. Species 2,... 

Safety/Health and Environmental Affairs are often interwoven in practice, especially where process emissions, chemical exposure, and waste disposal can impact on public health. Many, if not most, companies with chemical synthesis plants in populated areas work with local communities to foster good relations sometimes via open house days or in the creation of action plans to deal with adverse events which may occur in plant operation. The presentation on Environment (Chapter 5) addresses the canon that has developed to deal with exposure to chemicals, with the impact of spills and emissions on all life forms and with waste recycle, treatment, and disposal. 

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