Ring expansions of acyloxy nitroso compounds

Abstract

Treatment of cyclopentanone and cyclobutanone-derived oximes with lead (IV) tetraacetate gives the bright blue acyloxy nitroso compounds, which upon basic hydrolysis yields the ring expansion product cyclic hydroxamic acids in 12-81% yield. Reactions of substituted cyclopentanones provide ring expanded products where the -NOH group regioselectively inserts to the more substituted position and gives a better yield compared to the treatment of the same ketone with a basic solution of Piloty's acid. Reaction of phosphines with acyloxy nitroso compounds generally generates a ring-expanded Beckmann rearrangement product that can be hydrolyzed to the corresponding lactam. Acyloxy nitroso compounds that undergo rapid hydrolysis to HNO do not show this ring expansion reactivity. These results further demonstrate the versatility of acyloxy nitroso compound to yield structurally complex materials.

Keywords: Acyloxy nitroso compounds; Cyclic hydroxamic acids; HNO donors; Organic phosphines; Ring expansion.

Figure 1

X-Ray Crystallography data for hydroxamic acids 3c and 3e.

Scheme 1

Pathways of acyloxy nitroso compound hydrolysis.

Scheme 2

Conversion of ketones to cyclic hydroxamic acids via acyloxy nitroso compounds.

Scheme 3

Reaction of 1-nitrosocyclohexyl acetate (1) with TPP.

Scheme 4

Proposed mechanism for the reaction of 1-nitrosocyclohexyl acetate (1) with TPP.

Scheme 5

Reaction of NCA and NCP with TPP.

Scheme 6

Reaction of 12 with TXPTS in 1:1 acetonitrile: Tris buffer (0.1 M, pH 7.6).