Three-carbon ring expansion

Fused methylenecyclopentanes of type 9 in which n = 3 or >6 when treated with KH and 18-crown-6 undergo a three-carbon ring expansion to give products of type 10 in about 90% yield. This ring expansion was used to convert the /f-keto sulfone (11)... 

Reaction of cyclopropenes with cyclopropenium ions leads to a three carbon ring expansion to aromatic derivatives, presumably through ring opening of an initially formed cyclopropenyl-cyclopropylcation 276) ... 

Similar ring expansions are observed when 3,3 -bicyclopropenyls are treated with silver ion (see section 9). Reaction of the propanoic acid derivative (352) with oxalyl chloride also leads to a three carbon ring expansion, although the detailed mechanism of the reaction is not clear 212) ... 

The most general methods for preparing seven- or eight-membered rings from enamines are by ring expansion of the cyclobutene, cyclobutanone or chlorocyclopro-pane adducts formed by cycloaddition of acetylene carboxylates, ketenes or chlor-ocarbenes, respectively, to enamines of cyclopentanone or cyclohexanone. These are two-carbon or one-carbon ring expansions. Three-carbon ring expansions can also be carried out by cycloaddition of activated cyclopropenes or cyclopropenones. 

Bicyclo[10.3.0]-A -pentadecen-14-one (25) was prepared from cyclododecanone. Allylation of the 3-keto ester (23) and the oxidation of the terminal alkenic bond afforded the 1,4-diketone (24) in 72% yield from the 3-keto ester. Base-catalyzed cyclization and deethoxycarbonylation gave die bicycloketone (25), which was converted to muscone (26 Scheme 7). Thus, this is a method for three-carbon ring expansion. 

Scheme 79 Three-carbon ring expansion by Type M rearrangements...

This product was the starting material for Problem 5 in Chapter 38 and was used in a three-carbon ring expansion devised by B. M. Trost and J. E. Vincent, J. Am. Chem. Soc., 1980, 102, 5680. 

Formation of Six-Membered Rings 3.3.1. Carbocycles 3.3.1.1. Three-Carbon Ring Expansion... 

A three-carbon ring expansion also occurred in the case of the 3-allylcyclopropene 9. 3,4-Dimethyl-1,2-diphenylbenzene was the sole product, albeit in poor yield (25%). ... 

One of the best examples for three-carbon ring expansion is the total synthesis of DL- and (/ )-muscone starting from a cyclododecanone derivative [5, 13], A good yield of ring expansion product is obtained by the use of selenide as the radical precursor (Scheme 8). 

Three-carbon ring expansion was carried out in two stages. First, two-carbon homologation of the exo methylene ketone 8 followed by trapping of the intermediate etiolate as the criflate led to 9. Nozaki-Hiyama-Kishi coupling followed by acetylation smoothly converted 9 into 10. 

The reaction of acetyl-substituted aminopyran (101) with arylidenemalonitrile (102) afforded a novel bridge-head azocine (103) (Equation (14)). The controversy over its structure was resolved by x-ray crystallography <92T1581>. A one-pot, decarboxylative three-carbon ring expansion of a cyclic secondary amino acid afforded a tetrahydroazocine derivative <87CC1296>. 

Xie ZF, Suemune H, Sakai KJ (1988) Synthetic Approach to Medium-sized Cycloalkanones. A One-pot Three-carbon Ring Expansion of Carbocyclic p>-Keto Esters. J Chem Soc Chem Commun 612... 

Upon reaction with f-BuOK/DMSO, medium-ring /3-keto esters containing 4-oxopentyl side chains undergo three-carbon ring expansion reactions via an aldol-retroaldol process (eq 20). Similar reactions of related cyclic ketones containing electron-withdrawing a-substituents occur in t-BuOK/THF. ... 

Scheme 8.12 Rh-catalyzed carbonylative three-carbon ring expansion of allenylcyclobutane.

Cyclododecanone, which became the most accessible of medium-ring ketones following Wilke s discovery of the butadiene-cyclotrimerization process, is an important starting point for manufacture of the valuable musk ketones. Two syntheses of muscone, commencing from cyclododecanone are outlined below. The first synthesis, which emanated jointly from Eshenmoser s group in Zurich and laboratories of the Swiss perfume firm, Firmenich Cie., illustrates a three-carbon ring expansion reaction based on the widely applicable tosylhydrazone version of the oxidoketone— alkynone fragmentation. ... 

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