Alder addition

Four ring forming transforms have been considered at length by the LHASA development group - the Diels Alder addition, the Robinson Annelation, the Simmons-Smith reaction, and iodo-lactonization. The first three of these have been fully implemented in LHASA and the fourth is completely flow charted and awaits only coding into the chemistry data base language. 

ACS Symposium Series American Chemical Society Washington, DC, 1977. 

All ring chemistry tables are organized into what is called binary search trees. Queries are posed about the existence of certain structural features. Each of these questions is answerable with a yes or a no. Based on the answer one of two different followup questions is selected. Embedded within the table may be requests for subgoals, either those already in the PGI or PGA table or for special reactions which are needed only for these transforms and are not of general synthetic interest. 

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Aldrin is obtained from the Diels-Alder addition product of cyclopentadiene and vinyl chloride by dehydrochlorination followed by condensation with hexachlorocyclopenta-diene. 

Dramatic rate accelerations of [4 + 2]cycloadditions were observed in an inert, extremely polar solvent, namely in5 M solutions oflithium perchlorate in diethyl ether(s 532 g LiC104 per litre ). Diels-Alder additions requiring several days, 10—20 kbar of pressure, and/ or elevated temperatures in apolar solvents are achieved in high yields in some hours at ambient pressure and temperature in this solvent (P.A. Grieco, 1990). Also several other reactions, e.g, allylic rearrangements and Michael additions, can be drastically accelerated by this magic solvent. The diastereoselectivities of the reactions in apolar solvents and in LiClO EtjO are often different or even complementary and become thus steerable. 

The organotin maleate and maleate half-ester derivatives also exhibit this bleaching effect reportedly by a Diels-Alder addition reaction (18). The reaction is specific to the organotin maleates other organotin carboxylates containing normal dieneopltiles fail to produce similar results (19). 

V- Alkylpyrroles react with maleic anhydride to give the electrophilic substitution product (7) and not the Diels-Alder addition product found for... 

Most of the reactions of thiophosgene involve the expected chemistry of an acid chloride, in which the chlorine atoms are replaceable by various nucleophiles. A reaction involving the C=S bond is the Diels-Alder addition ... 

The Diels-Alder addition to 1,3-dienes is particularly interesting because of the exceptional ease with which it takes place, eg, see equation 1 in which l,2-dimethyl-4,4,5,5-tetracyanocyclohexene [69155-29-9] is formed. 

A -Amino- and A-substituted amino-pyrroles readily undergo Diels-Alder additions and add to activated alkynes at room temperature. The resulting azanorbornadienes extrude A-aminonitrenes and this forms the basis of an unusual synthesis of benzene derivatives (81S753,81TL3347). It has been found that ethyl/3-phenylsulfonylpropiolate (135) is a superior dienophile to DMAD (Scheme 50). 

Potential 2,5-dihydroxy compounds (185) exist in the dicarbonyl forms (186). Succinic anhydride (186 Z = O) on silylation is converted into 2,5-bis(trimethylsilyloxy)furan (187) the latter compound readily participates in Diels-Alder addition reactions (80TL3423). Reaction of thiosuccinic anhydride (186 Z = S) with the triphenylphosphorane Et02CH=PPh3 gives a product which exists in the aromatic form (188) (75LA1967). 

The Diels-Alder addition of maleic anhydride gave a compound for which two structures were proposed (Scheme 41) (66DIS(B)102,43JCS654). 

The monomer, norbomene (or bicyclo[2.2.l]hept-2-ene), is produced by the Diels-Alder addition of ethylene to cyclopentadiene. The monomer is polymerised by a ring-opening mechanism to give a linear polymer with a repeat unit containing both an in-chain five-membered ring and a double bond. Both cis-and trans- structures are obtainable according to the choice of catalyst used ... 

In 1980 the Goodyear company announced copolymers of cyclopentadiene, cyclo-octene or cyclo-octa-1,5-diene with the Diels-Alder addition product of hexachlorocyclopentadiene and cyclo-octa-1,5-diene. This material has been proposed as an alternative to the polychloroprenes, with lower ( 5°C), and superior ozone resistance... 

This trend is revealed, for example, by the rates of Diels-Alder addition reactions of anthracene, naphthacene, and pentacene, in which three, four, and five rings, respectively are linearly fused. The rate data are shown in Table 9.3. The same trend can be seen in the activation energy and the resonance energy gained when cycloreversion of the adducts 9-12 yields the aromatic compoimd, as shown in Scheme 9.3. 

Table 9.3. Rate of Diel-Alder Additions of Linear Polycyclic Aromatic Hydrocarbons"...

When benzyne is generated in the presence of potential dienes, additions at the highly strained triple bond occur. Among the types of compounds that give Diels-Alder addition products are furans, cyclopentadienones, and anthracene. 

The most important single reactions produced in the carboxyl functionality of the resin acids are salt formation, Diels-Alder additions, and esterification. Other reactions, such as disproportionation and polymerization, are less important. For some specific applications, rosins are subjected to a combination of these reactions. 

Tan et al. investigated polymers made from bis-benzocyclobutenes [13-15]. As the benzocyclobutane is analogous to tbe dien, tbe Diels-Alder addition takes place. This reaction is applied to the preparation of polyimides. The advantage of this system is that the resultant polymer is oxidized to form thermally stable aromatic polyimides (Fig. 7). 

Formal Diels-Alder additions of dienesters (111,332-335) and dien-ketones (336) to enammes have provided synthetic paths which may be applied to some natural products syntheses. However, a reaction of tetra-cyclone (330) gave only the cyclopentenone, rather than a Diels-Alder adduct. 

Simultaneously examine the HOMO of 1-methylcyclo-pentadiene (the diene) and the LUMO of acrylonitrile (the dienophile). Orient the two on screen such that they are disposed for Diels-Alder addition, i.e. 

Similarly, examine the overlap between the HOMO of 1-methylcyclopentadiene and the LUMO of an acrylonitrile BF3 complex. Does the Lewis acid affect overlap Would you expect BF3 to enhance, retard, or leave unchanged the rate of Diels-Alder addition ... 

Check your predictions by calculating activation energies for Diels-Alder additions. Data for transition states 1-methylcyclopentadiene+acrylonitrile and 1-methyl-cyclopentadiene+acrylonitrile BF3 are available. 

LUMO for acrylonitrile receives electrons in a Diels-Alder addition. 

A useful and possibly more general alternative to the Lwowski synthesis- of 1,3-diphenylisoindoles involves condensation of a l,2-dibenzoyl-l,4-cyclohexadiene (e.g., 55) with ammonia or a primary amine. Cyclohexadiene derivatives of this type are easily prepared by Riels-Alder addition of a 1,3-diene to dibenzoylacetylene, and these adducts lead directly, and in high yield, to the corresponding isoindoles (56). The reaction is closely related to the well-known synthesis of pyrroles by condensation of 1,4-diketones with ammonia. 4,7-Dihydro- and 4,5,6,7-tetrahydroisoindoles (57 and 58) have been... 

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