Abstract
The mesylate derivative of cis-1-hydroxymethyl-2-trimethylsilylcyclopropane has been prepared, along with a number of related mesylates and triflates with substituents on the 1-position. These substrates all solvolyze in CD3CO2D to give products derived from cyclopropylcarbinyl cations that undergo further rearrangement to give 3-trimethylsilylcyclobutyl cations. These 3-trimethylsilylcyclobutyl cations are stabilized by a long-range rear lobe interaction with the γ-trimethylsilyl group. When the substituent is electron-withdrawing (CF3, CN, or CO2CH3), significant amounts of bicyclobutane products are formed. The bicyclobutanes are a result of γ-trimethylsilyl elimination from the cationic intermediate that has an unusually long calculated Si–C bond. The solvolysis chemistry of mesylate and triflate derivatives of trans-1-hydroxymethyl-2-trimethylsilylcyclopropane and 1-substituted analogs can be quite different since these substrates do not generally lead to 3-trimethylsilylcyclobutyl cations.
Highlights
Carbocations, positively charged trivalent carbon compounds and reactive intermediates, have continued to fascinate chemists since the early discoveries of tropylium [1,2] and trityl [3,4,5,6,7] salts
This article will deal with three types of carbocations that have been of intense and fundamental interest over the years, i.e., cyclopropylcarbinyl cations, electron-deficient cations, and silyl substituted carbocations
The goal was to evaluate the cyclopropylcarbinyl to cyclobutyl cation rearrangement. Can these substrates lead to γ-trimethylsilyl-substituted cyclobutyl cations 11 and what are the fates of such carbocations? Answers to these questions were sought
Summary
Carbocations, positively charged trivalent carbon compounds and reactive intermediates, have continued to fascinate chemists since the early discoveries of tropylium [1,2] and trityl [3,4,5,6,7] salts. Can these substrates lead to γ-trimethylsilyl-substituted cyclobutyl cations 11 and what are the fates of such carbocations? The small amount (4%) of elimination product 22 is a result of rearrangement of 26 to the β-trimethylsilyl cation 25 as described in Scheme 5. Ring expansion via migration of bond b in 43 gives the β-trimethylsilyl-stabilized cyclobutyl cation 45, and subsequent desilylation provides cyclobutene (35).
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