The room temperature hydrogenolysis by Li,llH,-AlC13 of ether solutions of a number of 1,3-dioxolanes has been studied.Electron donor substituents on the Cz atom of the ring accelerate while electron acceptor substituents on C2 retard the reductive ring cleavage. The same effect but to a lesser extent is observed when these substituents are attached to the C4 or Cg atom of the ring.When electron donor substituents are attached to C4, ring-cleavage occurs predominantly a t the Cz-O bond remote from the C 4 position. On the other hand, electron-withdrawing groups attached to C4 give predominantly scission of the Cz-0 bond closer t o the C1-substituted position. In contrast to this n1arl;ed control over the direction of ring cleavage exhibited by substituents on C4, those on C n generally have little or no elfect on the direction of ring opening.A mechallistic interpretation of the results is presented. IN'IRODUCTIONThe stability of acetals and lretals towards lithillin a l u~~i i n u~n hydride perillits their use a s a means of protecting a lcetone or aldehyde nioiety during hydride reduction of other functional groups in a molecule (1). However, in the presence of acidic reagents such as anhydrous aluminum chloride or boron trifluoride, lithium aluminum hydride reductively cleaves the acetal or lretal to a n ether (1-5). Eliel et al. (6) have recently examined the LiAlH4-AlC13 hydrogenolysis of a nuiiiber of cyclic acetals and ketals (1,3-dioxolanes and 1,s-dioxanes) and obtained a high yield of the corresponding hydroxyethers arising from the cleavage of either the Cz-O1 or C2-O3 bond according to equation (a).Two ~nechanisms for this reduction have been suggested (3). One i~lvolves hydride attaclr on the complex formed frotn the Lewis acid and the acetal, a conlplex which tends t o form the stabilized oxocarbo~iiuin ion (equation (b)). The other requires prior fornlation of the a-haloether, which is then reaclily reduced (equation ( 6 )

A series of simple aliphatic nitro compounds has been synthesized and tested for antimicrobial activity in vitro. Some of the compounds inhibit the growth of a broad range of fungi and bacteria including species of Pseudomonas. The most active compounds are alcohols containing the grouping -CBrN02-. Replacement of bromine by hydrogen, chlorine, or alkyl groups diminishes the activity. Structure-activity relationships are discussed.

In ether solution, 1,3-diosolanes are hydrogenolyzed faster by LiAII-Id-AlCl3 than are the corresponding 1,3-dioxanes. This difference is attributed to the relative ease of oxocarbonium ion formation in the rate-determining step of the reaction. The results obtained have been utilized to explain the selective cleavage of the five-and six-membered acetal structures found in the polyacetals of hexitols.

Hydrogenolysis by LiAlH4-AIC13 of ether solutions of the cis and t r a m isomers of both 2,4-dimethyl-1,s-dioxolane and 2-ethyl-4-methyl-1,s-dioxolane have been carried out.T h e cis isomers are hydrogenolyzed respectively about 6.8 times and 10 times faster than are the corresponding trans isomers. The ratio of C?-01 t o C~0 3 bond cleavage in the cis isoiners is a t least 15 t o 1 while that for the trans isomers is about 1 t o 2. Isomerization during the aluminium chloride catalyzed hydrogenolysis is not detectable for the trans isomers. Slight indications of isomerization are discerned for the cis isomers.

.A number of 1,3-oxathiolanes and l,3-dithiolanes were subjected t o reduction in ether solution by lithium aluminum hydride in the presence of either aluminum chloride or boron trifluoride. Both of these Lewis acids not only isomerized 1,3-oxathiolanes but also catalyzed their hydrogenolysis to the hydroxy thioethers. Under the same conditions neither aluminum chloride nor boron trifluoride had any effect upon 1,3-dithiolanes. However, in methylene chloride solution, 1,3-dithiolanes are isomerized by both Lewis acids although their hydrogenolysis was not achieved, probably due t o the insolubility of the hydride in methylene chloride.A mechanistic interpretation is discussed to explain the results obtained.