Hann-Hudson rules

Hann, Hudson and their coworkers63 71 observed that the Hann-Hudson rules, although primarily based upon structures of known methylene acetals, were compatible with such of the structures of analogous benzylidene acetals as were then known. It was obvious when the rules were formulated that they did not apply at all to isopropylidene ketals. 

Rules (1) and (2) and part of rule (3) are essentially a restatement of the Hann-Hudson rules and the later extension of them that was made by Hann, Ness and Hudson.71 To these we have added rules (4), (5) and (6) rule (5) is to be regarded as tentative at the moment because the only syntheses upon which it can be based are those of l,5-dibenzoyl-2,3-benzyli-dene-arabitol, l,6-dibenzoyl-3,4-benzylidene-mannitol, and 1,6-dichloro-1,6-didesoxy-3,4-ethylidene-mannitol. 

A recent important extension of the Hann, Tilden and Hudson rule has its origin in their observation that a reducing substance is produced by the action of Acetobacter suboxydans on L-fucitol this result was confirmed by Bollenback and Underkofler.167 Inspection of the stereoformula of L-fucitol (XCIII) shows a trans position for the hydroxyl... 

L-fucitol by it conforms with this extended interpretation of the Hann, Tilden and Hudson rule. Further studies of the action, or lack of action, of Acetobacter suboxydans on other w-deoxy-alditols are being reported169 and so far they indicate the general applicability of the rule under the extended interpretation that a terminal methyl group is to be regarded as qualitatively equivalent to a hydrogen atom, insofar as the specificity of the oxidation by Acetobacter suboxydans is concerned. 

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