Dichlorocarbene, insertion

Predictably, the reaction of A V-disubstituted enamines [26-29] and non-conju-gated unsaturated amines with dihalocarbenes results in the exclusive formation of the dihalocyclopropane derivatives (see Section 7.3). Dichlorocarbene inserts into the a-CH bond of Af-alkyldibenzo[6,/]azepines [16], in addition to the expected electrophilic addition to the C=C bond (see Sections 7.2 and 7.3). 

Germylene insertion into germacyclobutanes to give 1,2-digermacyclopentanes has already been described (Scheme 88). However, the tetraethyl derivative (95) is better made via the mercury derivative (Scheme 162). Like its silicon counterpart, (95) is slowly oxidized at room temperature, and inserts sulfur, selenium and bromine in the Ge—Ge bond. While (95) is less stable than the 1,2-digermacyclohexane, dichlorocarbene inserts into the /3-C—H bond of both rings, and not the Ge—C bond (Scheme 163) (69JOM(16)227). 

The next step is dichlorocarbene insertion into the more nucleophilic of the two alkenes. J hlorocarbene is an electrophilic carbene so the main interaction is between the HOMO (ti) of r.e alkene and the empty p orbital of the carbene. The carbene is formed by decarboxylation, a process that needs no strong base. 

Dichlorocarbene inserts into allyl sulfides (67) via the Stevens rearrangement of the ylide intermediates. Internal competition for a carbene is always won by sulfur atom over olefins (68, 69), even though attack on sulfur would give rise to strained molecules. 

The dichlorocarbene insertion reaction has been studied primarily with hydrocarbons and a number of examples are recorded in Table 3.1. Also included in this table are several examples of insertion reactions which occur alpha to ether oxygen or a tertiary nitrogen. 

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