Photodecarbonylation of crystalline beta,gamma -unsaturated ketones and its application to preparative scale synthesis of adjacent quaternary centers
Reactions in crystals often proceed with selectivity and efficiency that rival enzymatic processes. Our group is developing the photochemical decarbonylation of crystalline ketones as a general strategy for the stereospecific construction of adjacent chiral quaternary centers. This thesis will discuss the advances and general applicability that have been made to advance this methodology and make it a more robust synthetic method.
Chapter 1, will provide a comprehensive review of photochemical decarbonylation in crystals. The factors that will be discussed include reactions in crystals, phase transitions, and ketone α-substituents. This will give the reader an understanding of the scope of this novel synthetic method, including its advantages and limitations. Chapter 1 will set the stage for the developments that will be presented in the remainder of the thesis. The history of photochemical decarbonylation from its earliest beginnings in the 1960's through 2005 will be elaborated.
The photochemistry and synthesis of 2-(cycloalken-1-yl)cycloalkanones will be discussed in Chapter 2. Factors that influence the reactivity of β,γ-unsaturated ketones will be discussed, including competing reactions. Chapter 3, will deal mainly with the synthesis of β,γ-unsaturated ketones. The beginnings of synthetic routes to optically active compounds are described. A novel variation of Michael reactions between imines and alkynes, to give bis-β,γ-unsaturated ketones, was used to synthesize decarbonylation precursors. The development of enantioselective versions of these reactions which could then undergo decarbonylation to give the optically active cyclopentane products is an important focus of this chapter. Crystal engineering and the preparative scale potential of decarbonylation in crystals of the compounds synthesized in Chapter 3 will be described in Chapter 4.
Chapter 5 discusses the synthesis and photochemistry of α-cyclopropyl ketones and cyclopropenones. These systems exhibit interesting behavior due to ring strain. α-Cyclopropyl ketones can potentially be used as radical clocks to understand the time scales involved in the decarbonylation reaction.