Substituted monocycles

Electrophilic substitutions at the pyrrole nucleus were described only with 1,2-dihydropyrrolizines which react with the same regioselectivity as would do equivalently substituted monocyclic pyrroles. 

Neuzil, R.W. (1985) Separation of ortho bi-alkyl substituted monocyclic aromatic isomers. U.S. Patent 4,482,777. 

Alkylation of enolates from substituted monocyclic lactams should furnish diastereomeric mixtures of products. For both racemic and nonracemic lactams, the potential of this type of reaction has not yet been fully exploited as few examples have been reported. One is alkylation of the racemic enolates derived from 1-substituted 5-ethoxy-2-pyrrolidinones16 18. 

To our knowledge, the first examples of asymmetrically substituted monocyclic phosphoranes are 60 and 61, described by Moriarty et al.135 and involving the reaction of a substituted o-benzoquinone136,137 (Scheme 6) on an aminophosphine (59), itself obtained by alcoholysis of 58 with l-( — )-menthol. In contrast to the amino phosphine 53 (Scheme 5), 59 is a mixture of the diastereoisomers 59a and b, and its reaction with 3,5-di-tert-butyl-l,2-benzoquinone yields two diastereoisomeric phosphoranes, 60a and b. Finally, alcoholysis of the P(V)—NR2 bond138 in 60a and b leads to 61a and b or 62. 

Monocyclic l,2-dihydro-l,2-azaborines (3) easily form polymers with the exception of the 2-phenyl derivative (109 R = Ph), probably because of interaction between the two rings. In contrast, the alkyl substituted monocyclic system (155) is stable towards polymerization although it is easily oxidized by air and hydrolyzed by water. This stability order between (3) and (155) was predicted by semi-empirical methods. However, the ring system (7), isosteric with pyridine, seems to be the most stable of the monocyclic systems. Some of its alkyl derivatives remain unchanged after 50 h in concentrated sulfuric acid at 80 °C. After reflux in 1M sodium hydroxide almost all of the compound was recovered. 

Substituted polycyclic hydrocarbons are named according to the same principles as substituted monocyclic hydrocarbons (see Rules A-12 and A-61). 

Intermediate formation of a(a )-methylenepyrans was also proposed for the isotopic-exchange reaction in the alkyl-substituted monocyclic py-... 

Interestingly, a-carboxy-substituted monocyclic pyrylium salts 195, probably because of a lower tendency towards nucleophilic addition in comparison with 2-benzopyrylium salts (Section III,C,1), react via two pathways. One is similar to reactions of 2-benzopyrylium salts (a), and the other resembles the behavior of isoquinolinium salts (b) (Section III, C,4,a,ii). In this case, monocyclic five-membered acyloins 198 were obtained in 15-40% yield. Obviously, their formation occurs by initial addition of amine (pathway a). The difficultly obtainable a-unsubstituted py-... 

The precursors 86 (n = 0) are accessible from purposely substituted monocyclic /3-lactams 88 and 89 by fused ring cyclization (see Section 2.03.9), in agreement with Baldwin s rules (Scheme 45) <1982CC1119, 1984TL4171, 1987PAC467>. 

In contrast to unsymmetrically substituted monocyclic tropolones (which usually give two isomeric derivatives), both benzo- and heterocyclotropo-lones form only one product, owing to the resonance inhibition of the tropolone ring. 

The most common routes to the bicyclic systems discussed in this chapter involve the reaction of suitably substituted monocyclic parents. In this section the formation of the second heterocyclic ring is considered methods of synthesis of the first ring can be found by consultation of Volumes 3 and 4 and CHEC-II or in CHEC-I. 

The azido olefins 117 and 120 were cyclized to the triazolines 118 and 119 in excellent yields <2001TL9175>. This is an interesting process in that the intermediate triazolines are isolated and then photolytically decomposed to aziridines 119 and 122 in very good yields (Scheme 19). All of these aziridines were reported to be stable compounds especially to acidic conditions. This is significant in that previous examples of silyl-substituted monocyclic aziridines were quite unstable undergoing acid-catalyzed rearrangements. 

The stereochemical course of SDNC with ring-substituted monocyclic precursors has been studied in detail. The choice between the two allowed comotations is influenced by (i) ring size (ii) substituent location (iii) substituent size and (iv) silyl group size. 

Substituted monocyclic phenols have been widely studied on several stationary phases (alumina, silica gel, cellulose, polyamide, silanized silica gel) and also on chemically modified adsorbents (cyano- and amino-silica plates), ion-exchange layers, and impregnated plates. 

Table 1 reports the retention data relative to some substituted monocyclic phenols examined on silica gel in benzene and diisopropylether. 

In general, cyclobutanones are synthesized by either ketene cycloadditions or by ring expansions of cyclopropyl precursors. For the synthesis of simple a-substituted monocyclic cyclobutanones, the latter method is usually employed, and a variety of approaches have been used to prepare the required eyclopropyl intermediates. 

Both substituted monocyclic and annulated cycloheptadienes are available by the rhodium-promoted rearrangement of divinylcyclopropanes of type 19. 

Basak, A. Bdour, H.M. Shain, J.C. Mandal, S. Rudra, K.R. Nag, S. DNA-cleavage studies on N-substituted monocyclic enediynes Enhancement of potency by incorporation of intercalating or electron poor aromatic ring and subsequent design of a novel phototriggerable acyclic enediyne. Bioorg. Med. Chem. Lett. 2000, 10, 1321-1325. 

The kinetics of the reactions of many xenobiotics with hydroxyl and nitrate radicals have been examined under simulated atmospheric conditions and include (1) aliphatic and aromatic hydrocarbons (Tuazon et al. 1986) and substituted monocyclic aromatic compounds (Atkinson et al. 1987c) (2) terpenes (Atkinson et al. 1985a) (3) amines (Atkinson et al. 1987a) (4) heterocyclic compounds (Atkinson et al. 1985b) and (5) chlorinated aromatic hydrocarbons (Kwok et al. 1995). For PCBs (Anderson and Hites 1996), rate constants were highly dependent on the number of chlorine atoms, and calculated atmospheric lifetimes varied from 2 days for 3-chlorobiphenyl to 34 days for 2,2, 3,5, 6-pentachlorbiphenyl. It was estimated that loss by hydroxylation in the atmosphere was a primary process for removal of PCBs from the environment. It was later shown that the products were chlorinated benzoic acids produced by initial reaction with a... 

---