A new geminal alkylation procedure based upon cyclobutanone spiroannelation with diphenylsulfonium cyclopropylide and I-lithiocyclopropyl phenyl sulfide followed by cyclobutane ring cleavage replaces the C-0 bonds of a carbonyl group by C-C bonds. Facilitation of ring cleavage by introduction of sulfur substituents CY to the carbonyl group of the cyclobutanone is required. The nucleophiles that initiated ring cleavage include hydroxide, methoxide, and methyllithium. In this way, a carboxylic acid or ester or ketone possessing the dithiane derivative of CHlCHO in the a position is created. While the versatility of this type of functionality is broad, it has been specifically demonstrated for the creation of a-methyl carboxylic esters and a novel cyclopentenone synthesis. Since the cyclobutanone spiroannelation is highly stereoselective, this geminal alkylation procedure is highly stereoselective. Thus, syntheses of .methyl deoxypodocarpate from 4ap-methyl-1,2,3,4,4a,9,10,1 Oa-octahydro-I-phenanthrene and of 3-carbomethoxy-6,10-dimethylspiro[4.5]dec-6-en-l -one, a potential precursor of hinesol, from 2,6-dimethylcyclohex-2-enone are described.The overall transformation represented by eq 1 involves the net replacement of the carbon-oxygen bonds of a carbonyl group with carbon-carbon bonds, a geminal alkylation. In the preceding paper, the cleavage is accomplished utilizing X = Br.3 Several limitations of the method are obvious. For example, the rigorousness required to achieve geminal bromination would eliminate the presence of isolated double bonds in the substrate. Cyclobutanones obtained by spiroannelation of aldehydes would brominate preferentially at the more substituted rather than less substituted side. A further complication involves the competition between ring cleavage and ring regression (semibenzylic acid rearrangement) with 1. Methods to overcome these prob-1 lems become even more important since cyclobutanones are also easily available from olefins as well as carbonyl partn e r~.~ These procedures can become stereospecific olefinic alkylations. In this paper, we wish to report in detail our results which attack this problem.Sulfur, like bromine, is an anion-stabilizing group but, unlike bromine, is a poor leaving group. Introduction of a geminal sulfur grouping should facilitate ring cleavage but preclude the reaction of ring regression. Equation 2 outlines the approach.The cyclobutanones employed in this study, 2-6, were prepared as previously reported utilizing diphenylsulfonium cycl~propylide~ or 1 -1ithiocyclopropyl phenyl sulfide6 followed by rearrangement of the initial adducts. We have recently discovered that lithium fluoroborate' is a superior acid catalyst for the rearrangement of oxaspiropentanes to cyclobutanones. Its advantages lie in its greater reproducibility, its faster rates, and its higher solubility in hydrocarbon solvents compared with lithium p e r~h l o r a t e .~.~ Although rearrangements were normally effected in refluxing benzene, room temperature also suffices with increased ...
