Extrusions of dibromocarbene under neutral conditions

Abstract

The thermal and photochemical decompositions of 5 have been studied. Both reactions lead to CBr2 transfer in good to high yields. With the 2‐pentenes as substrates, CBr2 transfer is stereospecific in the classical singlet carbene manner.

Carbenes from cyclopropanated aromatics

“…Some twenty years later, Warner and coworkers disclosed that photolysis or pyrolysis of 106 produced dibromocarbene ( 107 ) and indane ( 105 ) as shown in Scheme 23. 74 The carbene could be trapped by cyclohexene to yield norcarane 108 in yields ranging from 10% at 120 °C to 56% at 147 °C. Trapping by cis - or trans -2-pentene occurred in a stereospecific fashion to afford the cyclopropanated adducts ( 109 ).…”

“…The synthesis of 106 , as shown in Scheme 24, 74 was accomplished by initially performing a Birch reduction on indane ( 105 ) to synthesize the diene 111 . 75 Subsequent addition of dibromocarbene to 111 occurred predominantly at the more nucleophilic, tetra-substituted double bond to form 112 .…”

“…75 Finally, oxidation of 112 with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) delivered the desired precursor 106 . 74 Due to the relative ease of synthesizing 106 , and its similar or improved ability to generate 107 compared to naphthalene-based analogues (see section 4), Warner and coworkers noted that the indane-based method for generating carbenes showed particular promise. 74…”