Indene, cyclopropane adduct

Interest in this reaction was revived when the relevance of a carbene mechanism was realized, particularly following the demonstration (cf. SectionI,B) of a similar ring expansion of indene to 2-chloro-naphthalene by dichlorocarbene via the cyclopropane adduct. Indeed, at this time Nakazaki suggested that these reactions occurred by the addition of dichlorocarbene to the indolyl anion and subsequent rearrangement to the indolenine and, with loss of chloride ion, to the quinoline [Eq. (12)]. The preference of dichlorocarbene for... 

There are several phase transfer cyclopropanation reactions which deserve special comment. For example, addition of dichlorocarbene to the conjugated carbon-carbon double bond of styrene systems goes in excellent yield. Addition of dichlorocarbene to 1,2-dihydronaphthalenes [24] and to indenes [23] led to the expected 1,1-dichlorocyclopropane adducts. Heating the 1,1-dichlorocarbene adducts of indenes with ethanolic KOH provides an efficient route to 2-chloronaphthalene derivatives [23] (see Eq. 2.14). 

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