Silicon-Oxygen Heterocycles from Thermal, Photochemical, and Transition-Metal-Catalyzed Decomposition of α-(Alkoxysilyl and Alkenyloxysilyl)-α-diazoacetates

Abstract

Photolysis of (ethoxy)silyl‐, (propyloxy)silyl‐, and (isopro‐pyloxy)silyl‐substituted diazoacetates 1a–c leads to tetrahydro‐1,2‐oxasiloles 2a–c by intramolecular C–H insertion of a carbene intermediate. Photochemical or catalytic decomposition of (allyloxysilyl)diazoacetates 3a–e results in intramolecular cyclopropanation which provides 3‐oxa‐2‐silabicyclo[3.1.0]hexane systems 5a–e. In contrast, the thermal reaction of 3b–d gives rise to 2,5‐dihydro‐1,2‐oxasiloles 4b–d, which are likely to be formed on a pyrazoline rather than a carbene route. For (3‐butenyloxysilyl)diazoacetate 3f, all modes of decomposition generate the 3‐oxa‐2‐silabicyclo[4.1.0]heptane system 7. Fluoride‐induced cleavage of the bicyclic systems 5b–d provides trans‐2‐hydroxyalkyl‐1‐cyclopropanecarboxylates 9 diastereospecifically.

Novel photochemical reactions of carbocyclic diazodiketones without elimination of nitrogen – a suitable way to N-hydrazonation of C–H-bonds

“…On direct irradiation of tricyclic diazodiketones 1 possessing endo -configuration ( Fig. 2 ), one would expect in addition to the Wolff rearrangement also the occurrence of an intramolecular cyclopropanation (with 1b , d , e ) [ 53 – 55 ] or an insertion of the assumed intermediate dioxocarbenes in C–H-bonds at С 5 or С 6 -atoms (with 1c ) [ 26 , 42 – 45 ]. However, the performed experiments did not confirm the formation of corresponding reaction products in the photochemical reactions studied.…”

Intramolecular Photochemical C−H Insertions of α‐Diazocarbonyl Compounds

“…In 1999, Maas et al reported the photochemical intramolecular CÀ H insertion of α-(alkoxysilyl)-α-diazoacetates 40 to yield tetrahydro-1,2-ozasiloles 41 (Scheme 12). [18] They found improved yields of 41 were achieved by employing lower concentrations of diazo starting material (0.06 M) and irradiation with a 254 nm light source rather than a light source with λ max � 300 nm.…”