Group 13 systems unsaturated rings

An acetoxyl group at C-21, if present, is retained and an a,) -unsaturated ketone system in ring A does not interfere. 

The molecule under subject is a push-pull system which contains a benzene ring with either a donor group D (i.e. an electron-rich fragment) and an acceptor group A (i.e. an electron-poor fragment) which are positioned at the opposite sides of the 7i-unsaturated ring.69... 

The aromatic hydrocarbons contain at least one unsaturated ring system with the general structure C6R6, where R is any functional group (see Chap. 1). The parent hydrocarbon of this class of compounds is benzene (C6H6), which exhibits the resonance, or delocalization of electrons, typical of unsaturated cyclic structures. Owing to its resonance energy, benzene is remarkably inert. 

Fozard and Jones (65JOC1523) have discussed the then hypothetical, maximally unsaturated ring system of pyrido[l,2-fl]azepine (1). Because a fully aromatic form of the parent substance must be excluded they expected some stabilization by a hydroxy group attached to the 10-position, in this... 

Parent a,/3-unsaturated system a-Ring residue, R )3-Alkyl group (two methyls) Exocyclic double bond Solvent correction (hexane) 215 nm 10 24 5 -11 Calcd A, xx 245 nm found 244 nm... 

Claims for the synthesis of small unsaturated ring systems containing a metalloid atom have an interesting history. In the early 1960s, a series of papers appeared describing the products of reaction of Group IV analogs of carbene with tolan 197, 208, 346, 350-353) ... 

Treatment of alkanoic acids with thionyl chloride and a catalytic amount of pyridine causes oxidation at the a-methylene group and the formation of an a-chloro-a-(chlorosulphenyl)acyl chloride, RCHiQSCOCICOCl. This usually reacts further and when R contains a benzene ring, this may be attacked with consequent formation of a fused ring system.. Unsaturated aralkanoic acids behave similarly. Extension of this work to related compounds suggests that a concerted elimination-cyciization operates. 

Starting from vinylsulfonamides bearing a suitable leaving group such as halogen at the alkene moiety affords the 5,6-unsaturated ring system. Thus, 2-chloro-2-phenylvinylsulfonamidc reacts with methyl isothiocyanate and anhydrous potassium carbonate in acetone (50-55 °C for 3 h)... 

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