Cycloheptanone dimethyl acetals

In hydrogenolyses with HAICU, the dimethyl acetals of cyclobutanone and cyclohexanone are cleaved more slowly than that of 3-pentanone, while those of cyclopentanone and cycloheptanone are cleaved more rapidly (Table 1), as would be expected for a carbonium ion process. The differences in rate are small, suggesting that carbonium ion character is not strongly developed in the transition state. With the dimethyl acetal of 4-t-butylcyclohexanone, the hydride addition step occurs with strongly predominating axial addition when HAlCh is used Zn(BH4)2 with TMS-Cl, and TMS-H with TMSO-Tf are less selective (Table 2). Equatorial attack predominates, however, in the reduction of the ketone itself with TBDMS-H and TBDMS-OTf. ... 

Under slightly different conditions, using 1,3-propanedithiol, acyloins and acyloin acetates lead to the formation of 1,3-dithianes where hydrogen has replaced the hydroxyl or acetoxyl groups . Hydrolysis to the ketone provides a method of converting acyloins to ketones and desulphurization allows conversion of acyloins to hydrocarbons (equation 10). Reduction of l,l-dimethyl-5-hydroxysila-4-cycloheptanone gave l,l-dimethylsila-4-cycloheptanone by this method (equation 11) . A similar reaction is believed to be involved in the action of D-proline reductase . ... 

Bromocycloheptanone is reduced to cycloheptanone by titanocene dichloride and magnesium. Vinyl acetates, including 1- and 2-acetoxycyclohepta-1,3-dienes, have been prepared from vinyl bromides using copper(i) acetate. a-Formylcyclo-heptanone reacts with 2,2-dimethyl-3-dimethylamino-2ff-azirine to give adduct (320). Electrochemical reduction of some seven-membered cyclic P-diketones has been studied polarographically/ ... 

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