Ketones, monocyclic halo

Dihalides and 1,5-ditosylates have been used for the preparation of fully-saturated monocyclic 1,2-diazepines 165 (Scheme 83). 5-Halo-aldehydes and 5-halo-ketones react with a wide range of substituted hydrazines to give 4,5,6,7-tetrahydro-l,2-diazepines 166 <1976H(4)1509>. The reaction of 1,5-diketones with hydrazine has been much used as a source of 5,6-dihydro-4/7- 1,2-diazepines 167 . 

Tri-n-butyltin hydride, which selectively reduces aldehydes in a mixture with ketones if it is absorbed on silica gel, efficiently reduces penicillins to 4-sub-stituted monocyclic azetidininones, and reduces the carbon-halo n bond. The phenylselenides and selenoacetals derived directly from alcohols or ketones can be reduced to the hydrocarbon in high yield using PhsSnH. ... 

Coates and coworkers recently reported that boron-based Lewis acids such as BCI3 (Equation 18) and BBrs (Equation 19) react with various acyclic and monocyclic 5,c-unsaturated ketones (25) to give the halide-terminated syn-selective halo-Prins cyclization products, thus providing the sterically congested chlorohydrin (26) and bromohydrins (28) [24]. Here, the use of SnCU as a Lewis acid afforded the opposite selectivity to give the trans-chlorohydrin product (27) (Equation 18), highlighting the complementarity often possible with boron halides. 

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