Parent carbocyclic

The Parent Carbocyclic Subunit of Neocarzinostatin Chromophore A WenderTC, 1988,29,909. 

The main surveyed structural types are depicted in Figure 1. They are based on the parent carbocyclic benzoazulene core (Q — A = carbon) which produces a... 

As will be apparent, the (S) names for 21 and 24 are obtained by applying Stelzner replacement principles to Chemical Abstracts fusion names for the parent carbocycles. However, the Stelzner principles were originally intended to be applied to Stelzner fusion (SF) names, as shown in 21 and 24. 

For replacement names the parent carbocycles, apart from benzene, are all named as cycloalkanes (modified to -ene, -diene, etc., as necessary) with the heteroatom replacing /CH2, CH, or C— as appropriate to its valency. Replacement names derived from benzene are not used unless the three formal double bonds are retained otherwise names of the type oxacyclohexa-2,4-diene are appropriate [see 1-3 and 57-60 replacement names for 7-11 are thiacyclopenta-2,4-diene (7), 1,3-diazabenzene (8), l-oxa-2,5-diazacyclopenta-2,4-diene (9), l-oxa-4-azacyclohexane (10), and l,2-diazacyclopent-3-ene (11)]. 

Experimental data as well as calculations 284, 330) reveal two important differences between silicon-carbon bonds and carbon-carbon bonds, i.e., torsional barriers are small and gauche interactions unimportant for the Si—C bond when compared to the C—C bond. Low torsional barriers may imply a more flexible system (lower barriers to ring inversion), and small gauche interactions may imply lack of substituent preference or low substituent preference when compared to the parent carbocycle. Although calculations for heavier Group IV heteroatoms have not been published, it is probable that results will be similar to those obtained for Si. 

The conformational properties of eight-membered rings linearly fused with two benzene rings have been investigated in some detail by dynamic NMR. The parent carbocyclic compound is (452) which exists as a 1 1 mixture of the chair (453) and the boat (probably... 

Scheme 7-35 Synthesis of the parent carbocycle 150 of the NCS chromophore by photolytic ring contraction of the bis-propargylic sulfone 148 (Wender et al.).

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