Cycloalkene: functional group

The inhibitory effects of polar functional groups are not nearly as pronounced when the substituent is attached to a strained cycloalkene, where the release of ring strain provides a significant driving force for its metathesis. The norbornene ring system polymerizes easily by ring opening thus, numerous functionalized polymers have been prepared by the sequence depicted in Eq. (61). Many of these polymers hold some potential for commercialization and hence the bulk of this work is reported in the patent literature. 

The direct comparison of 1 and 2 in a variety of RCM reactions also indicates a presumably close relationship between these catalysts (Table 1) [6]. Both of them give ready access to cycloalkenes of almost any ring size > 5, including medium sized and macrocyclic products. Only in the case of the 10-membered jasmine ketolactone 16 was the yield obtained with 2a lower than that with lc this result may be due to a somewhat shorter lifetime of the cationic species in solution. However, the examples summarized in Table 1 demonstrate that the allenylidene species 2 exhibit a remarkable compatibility with polar functional groups in the substrates, including ethers, esters, amides, sulfonamides, ketones, acetals, glycosides and even free hydroxyl groups. 

The optimum catalyst for a given reaction depends primarily on (a) the energetics of the reaction and (b) the functional groups present in the substrate. If, for instance, a strained cycloalkene such as norbomene or cyclobutene is to be polymerized, a catalyst of low activity will be sufficient to attain acceptable reaction rates. RCM... 

The sequential addition method also allows the synthesis of many different block copolymers in which the two monomers have different functional groups, such as epoxide with lactone, lactide or cyclic anhydride, cyclic ether with 2-methyl-2-oxazoline, imine or episul-Hde, lactone with lactide or cyclic carbonate, cycloalkene with acetylene, and ferrocenophane with cyclosiloxane [Aida et al., 1985 Barakat et al., 2001 Dreyfuss and Dreyfuss, 1989 Farren et al., 1989 Inoue and Aida, 1989 Keul et al., 1988 Kobayashi et al., 1990a,b,c Massey et al., 1998 Yasuda et al., 1984]. 

Cycloalkenes are nonpolar molecules like alkanes. As a result, they tend to have low melting and boiling points compared with other functional groups. 

The ozonolysis of cyclohexene to 1,6-dioxygenated compounds is shown in Figure 17.28. Other cycloalkenes similarly afford other l,y-dioxygenated cleavage products. With the three methods for workup (Figure 17.27), this ozonolysis provides access to 1,6-hexanediol, 1,6-hexanedial, or to 1,6-hexanedicarboxylic acid. Each of these compounds contains two functional groups of the same kind. 

Alternating polymers can be produced by taking advantage of the functional group tolerance, high activity, and chemoselectivity of 3. Copolymerization of cycloalkenes such as cyclooctene or cyclopentene with diacrylates affords regular alternating polymers (Eq. 15) [32]. Based on the different reactivity of the two monomers (class 1 and class 2, respectively) the more... 

Remarkable development over the last 10-15 years in the synthesis of well-defined functional-group-tolerant ruthenium carbenes (Grubbs-related catalysts) also caused real development of the metathesis-based reactions in organosilicon polymers. For recent reviews on metathesis of organosilicon compounds see Refs. [6,7]. Unsaturated organosilicon polymers can be synthesized via ruthenium carbene catalyzed ring-opening metathesis polymerization (ROMP) of silylsubstituted cycloalkenes (Eq. 113). 

The oxidation of alkenes and cycloalkenes may affect the double bonds, the rest of the molecule, or both. Also included in this section are aromatic hydrocarbons containing double bonds in their side chains. Compounds containing double bonds and other functional groups, such as hydroxyl, carbonyl, or carboxyl, will be discussed in the appropriate sections, such as unsaturated alcohols, aldehydes, ketones, acids, and esters. 

Ruthenium salts such as Riidb.-xIf.O or ruthenium(ll) tosylates have been known for long to effectively catalyze ROMP of several cycloalkenes. Despite the characterization of several olefin-ruthenium(II) complexes [151-154], fhe actual catalytic species in such systems is still ill-defined. Nevertheless, fhe fact fhat ruthenium-based systems did effectively catalyze fhe ROMP even in aqueous systems [155, 156] or in the presence of ofher protic functional groups (alcohols, carboxylic acids, etc.) [153, 154, 157-162] initiated an intense search for well-defined, functional group-tolerant ruthenium systems [163], mainly conducted by the group of R.H. Grubbs. In 1992, this group described fhe synfhesis of the first well-defined ruthenium alkylidene (Scheme 5.12) [75]. 

Unsaturated compounds containing functional groups may be divided into four broad groups according to their effect on the ROMP of cycloalkenes (i) inhibitors ... 

The catalytic addition of organic and inorganic silicon hydrides to alkenes, ary-lalkenes, and cycloalkenes as well as their derivatives with functional groups leads to their respective alkyl derivatives of silicon and occurs according to the anti-Markovnikov rule. However, under some conditions (e.g., in the presence of Pd catalysts), this product is accompanied by a-adduct (i.e., the one containing an internal silyl group). Moreover, dehydrogenative silylation of alkenes with hydrosilanes, which proceeds particularly in the presence of iron- and cobalt-triad complexes as related to hydrosilylation (and very often its side reaction), is discussed. 

Synthetic Aspects of Hydrosilylation. The formation of the Si-C bond is based on the addition of the Si—H bond to the carbon-carbon bond of alkenes, arylalkenes, cycloalkenes, alkadienes and -trienes, and alkynes, as well as their derivatives with functional groups (3,64). 

The ruthenium-catalyzed hydrosilylation/protodesilylation protocol is a useful method for stereoselective internal alkyne (cycloalkyne) reduction to (E)-alkenes [(iJ)-cycloalkenes] and is a complement to the cis selectivity observed in the Lindlar reduction (eqs. (27) and (28)) (184,185). The utility of this reaction sequence is attributed to the fact that many of the knovra methods for transforming ahquies to ( )-alkenes either have poor selectivity or are incompatible with common functional groups. 

Wong, J.S., MacPhail, R.A., Moore, C.B., and Strauss, H.L., Local mode spectra of inequivalent C-H oscillators in cycloalkanes and cycloalkenes, J. Phys. Chem., 86, 1478-1484, 1982. Dannenberg, H., Determination of functional groups in epoxy resins by near-inflared spectroscopy, SPE Trans., 78-88, January 1963. 

There are three main transformations of the functional group interconversion (FGI), elimination (FGE) and addition (FGA), assigned by double arrows (Table 1.1). Another important retrosynthetic tool represents reconnection (RCN) of acyclic to cyclic structures. Reversal to a synthetic direction is the formation of an acyclic structure by ring opening. A typical example is reconnection of an a, co-dicarbonyl compound to cycloalkene, e.g., 1,6-hexanedialdehyde to cyclohexene. In the synthetic direction ozonolysis of the double bond in cyclohexene affords 1,6-dialdehyde. 

The sulphur and nitrogen heterocycles (80) and (81) have been prepared by hydroboration-carbonylation of bis-olefinic precursors, and the latter case is reported to be the first example of such a synthesis in the presence of a reducible functional group. Another hydroboration-carbonylation sequence has been used in the preparation of methylene cycloalkanes from cycloalkenes, and is shown in Scheme 11. ... 

A carbon-carbon triple bond is the functional group characteristic of the alkynes. The general formula for the alkynes is C H2 2, the same as that for the cycloalkenes. The common names for many alkynes are still in use, including acetylene, the common name of the smallest aUcyne, C2H2. Other alkynes are treated as its derivatives—for example, the alkylacetylenes. 

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