Chiral Polycyclic Ketones via Desymmetrization of Dihaloolefins

Abstract

3-Chloronorbornenone (R)-1a (98% ee) was obtained from trichloronorbornene 5 in two steps by the in situ generation of dichloronorbornadiene 2a with t-BuOK and desymmetrization with (-)-ephedrine, followed by hydrolysis with PPTS. The generality of this desymmetrization with (-)-ephedrine was tested with dibromonorbornadiene 2c and other substituted dichloronorbornadienes.

Synthesis and Diels–Alder cycloaddition reaction of norbornadiene and benzonorbornadiene dimers

“…Dehydrobromination reaction of dibromides 3 with potassium tert -butoxide resulted in the formation of monobromide 4 . The other starting material 5 was obtained using the reported procedures based on the use of potassium tert -butoxide/ n -butyllithium super-base by starting with commercially available norbornadiene [24–27]. …”

Trihaloethenes as versatile building blocks for organic synthesis

“…Another example of a [4 + 2] cycloaddition was published by Borsato (Scheme 17). 45 They synthesized 3-chloronorbornenone 46 The bicyclic enone 77 was dissolved in 1 and irradiated with a 500 W high-pressure mercury lamp. The following elimination of hydrochloric acid under basic conditions allowed isolation of the cyclobutene 78.…”

“…Another example of a [4 + 2] cycloaddition was published by Borsato (Scheme 17). 45 They synthesized 3-chloronorbornenone (76) via a three-step synthesis starting with a Diels-Alder reaction between TCE (1) and cyclopentadiene. The formed trichloronorbornene 72 was converted to the dichloronorbornadiene 73 under basic conditions and subsequently desymmetrized with the chiral auxiliary (−)-ephedrine (74).…”